Radical Ionic Systems: Properties in Condensed Phases (Topics in Molecular Organization and Engineer

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Sometimes the distinction between phases can be continuous instead of having a discrete boundary, in this case the matter is considered to be in a supercritical state. When three states meet based on the conditions, it is known as a triple point and since this is invariant, it is a convenient way to define a set of conditions. The most familiar examples of phases are solids , liquids , and gases.

Many substances exhibit multiple solid phases. For example, there are three phases of solid iron alpha, gamma, and delta that vary based on temperature and pressure. A principal difference between solid phases is the crystal structure , or arrangement, of the atoms. Another phase commonly encountered in the study of chemistry is the aqueous phase, which is the state of substances dissolved in aqueous solution that is, in water.

Less familiar phases include plasmas , Bose—Einstein condensates and fermionic condensates and the paramagnetic and ferromagnetic phases of magnetic materials. While most familiar phases deal with three-dimensional systems, it is also possible to define analogs in two-dimensional systems, which has received attention for its relevance to systems in biology. Atoms sticking together in molecules or crystals are said to be bonded with one another. A chemical bond may be visualized as the multipole balance between the positive charges in the nuclei and the negative charges oscillating about them.

A chemical bond can be a covalent bond , an ionic bond , a hydrogen bond or just because of Van der Waals force. Each of these kinds of bonds is ascribed to some potential. These potentials create the interactions which hold atoms together in molecules or crystals. In many simple compounds, valence bond theory , the Valence Shell Electron Pair Repulsion model VSEPR , and the concept of oxidation number can be used to explain molecular structure and composition.

An ionic bond is formed when a metal loses one or more of its electrons, becoming a positively charged cation, and the electrons are then gained by the non-metal atom, becoming a negatively charged anion. The two oppositely charged ions attract one another, and the ionic bond is the electrostatic force of attraction between them.

The ions are held together due to electrostatic attraction, and that compound sodium chloride NaCl , or common table salt, is formed. In a covalent bond, one or more pairs of valence electrons are shared by two atoms: Atoms will share valence electrons in such a way as to create a noble gas electron configuration eight electrons in their outermost shell for each atom. Atoms that tend to combine in such a way that they each have eight electrons in their valence shell are said to follow the octet rule. However, some elements like hydrogen and lithium need only two electrons in their outermost shell to attain this stable configuration; these atoms are said to follow the duet rule , and in this way they are reaching the electron configuration of the noble gas helium , which has two electrons in its outer shell.

Similarly, theories from classical physics can be used to predict many ionic structures. With more complicated compounds, such as metal complexes , valence bond theory is less applicable and alternative approaches, such as the molecular orbital theory, are generally used.

See diagram on electronic orbitals. In the context of chemistry, energy is an attribute of a substance as a consequence of its atomic , molecular or aggregate structure. Since a chemical transformation is accompanied by a change in one or more of these kinds of structures, it is invariably accompanied by an increase or decrease of energy of the substances involved. Some energy is transferred between the surroundings and the reactants of the reaction in the form of heat or light ; thus the products of a reaction may have more or less energy than the reactants.

A reaction is said to be exergonic if the final state is lower on the energy scale than the initial state; in the case of endergonic reactions the situation is the reverse. A reaction is said to be exothermic if the reaction releases heat to the surroundings; in the case of endothermic reactions , the reaction absorbs heat from the surroundings.

Chemical reactions are invariably not possible unless the reactants surmount an energy barrier known as the activation energy. This exponential dependence of a reaction rate on temperature is known as the Arrhenius equation. The activation energy necessary for a chemical reaction to occur can be in the form of heat, light, electricity or mechanical force in the form of ultrasound.

A related concept free energy , which also incorporates entropy considerations, is a very useful means for predicting the feasibility of a reaction and determining the state of equilibrium of a chemical reaction, in chemical thermodynamics. There exist only limited possible states of energy for electrons, atoms and molecules. These are determined by the rules of quantum mechanics , which require quantization of energy of a bound system.

The phase of a substance is invariably determined by its energy and the energy of its surroundings. When the intermolecular forces of a substance are such that the energy of the surroundings is not sufficient to overcome them, it occurs in a more ordered phase like liquid or solid as is the case with water H 2 O ; a liquid at room temperature because its molecules are bound by hydrogen bonds. The transfer of energy from one chemical substance to another depends on the size of energy quanta emitted from one substance.

However, heat energy is often transferred more easily from almost any substance to another because the phonons responsible for vibrational and rotational energy levels in a substance have much less energy than photons invoked for the electronic energy transfer. Thus, because vibrational and rotational energy levels are more closely spaced than electronic energy levels, heat is more easily transferred between substances relative to light or other forms of electronic energy.

For example, ultraviolet electromagnetic radiation is not transferred with as much efficacy from one substance to another as thermal or electrical energy. The existence of characteristic energy levels for different chemical substances is useful for their identification by the analysis of spectral lines. Different kinds of spectra are often used in chemical spectroscopy , e.

Spectroscopy is also used to identify the composition of remote objects — like stars and distant galaxies — by analyzing their radiation spectra. The term chemical energy is often used to indicate the potential of a chemical substance to undergo a transformation through a chemical reaction or to transform other chemical substances. When a chemical substance is transformed as a result of its interaction with another substance or with energy, a chemical reaction is said to have occurred. A chemical reaction is therefore a concept related to the "reaction" of a substance when it comes in close contact with another, whether as a mixture or a solution ; exposure to some form of energy, or both.

It results in some energy exchange between the constituents of the reaction as well as with the system environment, which may be designed vessels—often laboratory glassware. Chemical reactions can result in the formation or dissociation of molecules, that is, molecules breaking apart to form two or more smaller molecules, or rearrangement of atoms within or across molecules.

Chemical reactions usually involve the making or breaking of chemical bonds. Oxidation, reduction , dissociation , acid-base neutralization and molecular rearrangement are some of the commonly used kinds of chemical reactions. A chemical reaction can be symbolically depicted through a chemical equation. While in a non-nuclear chemical reaction the number and kind of atoms on both sides of the equation are equal, for a nuclear reaction this holds true only for the nuclear particles viz.

The sequence of steps in which the reorganization of chemical bonds may be taking place in the course of a chemical reaction is called its mechanism. A chemical reaction can be envisioned to take place in a number of steps, each of which may have a different speed. Many reaction intermediates with variable stability can thus be envisaged during the course of a reaction.

Reaction mechanisms are proposed to explain the kinetics and the relative product mix of a reaction. Many physical chemists specialize in exploring and proposing the mechanisms of various chemical reactions. Several empirical rules, like the Woodward—Hoffmann rules often come in handy while proposing a mechanism for a chemical reaction.

According to the IUPAC gold book, a chemical reaction is "a process that results in the interconversion of chemical species. An additional caveat is made, in that this definition includes cases where the interconversion of conformers is experimentally observable. Such detectable chemical reactions normally involve sets of molecular entities as indicated by this definition, but it is often conceptually convenient to use the term also for changes involving single molecular entities i.

An ion is a charged species, an atom or a molecule, that has lost or gained one or more electrons. When an atom loses an electron and thus has more protons than electrons, the atom is a positively charged ion or cation. When an atom gains an electron and thus has more electrons than protons, the atom is a negatively charged ion or anion.

Plasma is composed of gaseous matter that has been completely ionized, usually through high temperature. A substance can often be classified as an acid or a base. There are several different theories which explain acid-base behavior. The simplest is Arrhenius theory , which states than an acid is a substance that produces hydronium ions when it is dissolved in water, and a base is one that produces hydroxide ions when dissolved in water.

A third common theory is Lewis acid-base theory , which is based on the formation of new chemical bonds. Lewis theory explains that an acid is a substance which is capable of accepting a pair of electrons from another substance during the process of bond formation, while a base is a substance which can provide a pair of electrons to form a new bond. According to this theory, the crucial things being exchanged are charges. Acid strength is commonly measured by two methods. One measurement, based on the Arrhenius definition of acidity, is pH , which is a measurement of the hydronium ion concentration in a solution, as expressed on a negative logarithmic scale.

Thus, solutions that have a low pH have a high hydronium ion concentration, and can be said to be more acidic. That is, substances with a higher K a are more likely to donate hydrogen ions in chemical reactions than those with lower K a values. Redox red uction- ox idation reactions include all chemical reactions in which atoms have their oxidation state changed by either gaining electrons reduction or losing electrons oxidation.

Substances that have the ability to oxidize other substances are said to be oxidative and are known as oxidizing agents , oxidants or oxidizers. An oxidant removes electrons from another substance. Similarly, substances that have the ability to reduce other substances are said to be reductive and are known as reducing agents , reductants, or reducers. A reductant transfers electrons to another substance, and is thus oxidized itself.

And because it "donates" electrons it is also called an electron donor. Oxidation and reduction properly refer to a change in oxidation number—the actual transfer of electrons may never occur. Thus, oxidation is better defined as an increase in oxidation number , and reduction as a decrease in oxidation number. Although the concept of equilibrium is widely used across sciences, in the context of chemistry, it arises whenever a number of different states of the chemical composition are possible, as for example, in a mixture of several chemical compounds that can react with one another, or when a substance can be present in more than one kind of phase.

A system of chemical substances at equilibrium, even though having an unchanging composition, is most often not static ; molecules of the substances continue to react with one another thus giving rise to a dynamic equilibrium. Thus the concept describes the state in which the parameters such as chemical composition remain unchanged over time. Chemical reactions are governed by certain laws, which have become fundamental concepts in chemistry. Some of them are:. The definition of chemistry has changed over time, as new discoveries and theories add to the functionality of the science.

The term "chymistry", in the view of noted scientist Robert Boyle in , meant the subject of the material principles of mixed bodies. The definition of the word "chemistry", as used by Georg Ernst Stahl , meant the art of resolving mixed, compound, or aggregate bodies into their principles; and of composing such bodies from those principles. Early civilizations, such as the Egyptians [41] Babylonians , Indians [42] amassed practical knowledge concerning the arts of metallurgy, pottery and dyes, but didn't develop a systematic theory. A basic chemical hypothesis first emerged in Classical Greece with the theory of four elements as propounded definitively by Aristotle stating that fire , air , earth and water were the fundamental elements from which everything is formed as a combination.

Greek atomism dates back to BC, arising in works by philosophers such as Democritus and Epicurus. In the Hellenistic world the art of alchemy first proliferated, mingling magic and occultism into the study of natural substances with the ultimate goal of transmuting elements into gold and discovering the elixir of eternal life.

Boyle in particular is regarded as the founding father of chemistry due to his most important work, the classic chemistry text The Sceptical Chymist where the differentiation is made between the claims of alchemy and the empirical scientific discoveries of the new chemistry. The theory of phlogiston a substance at the root of all combustion was propounded by the German Georg Ernst Stahl in the early 18th century and was only overturned by the end of the century by the French chemist Antoine Lavoisier , the chemical analogue of Newton in physics; who did more than any other to establish the new science on proper theoretical footing, by elucidating the principle of conservation of mass and developing a new system of chemical nomenclature used to this day.

Before his work, though, many important discoveries had been made, specifically relating to the nature of 'air' which was discovered to be composed of many different gases. English scientist John Dalton proposed the modern theory of atoms ; that all substances are composed of indivisible 'atoms' of matter and that different atoms have varying atomic weights. The development of the electrochemical theory of chemical combinations occurred in the early 19th century as the result of the work of two scientists in particular, J.

Berzelius and Humphry Davy , made possible by the prior invention of the voltaic pile by Alessandro Volta. Davy discovered nine new elements including the alkali metals by extracting them from their oxides with electric current. British William Prout first proposed ordering all the elements by their atomic weight as all atoms had a weight that was an exact multiple of the atomic weight of hydrogen.

Newlands devised an early table of elements, which was then developed into the modern periodic table of elements [65] in the s by Dmitri Mendeleev and independently by several other scientists including Julius Lothar Meyer. At the turn of the twentieth century the theoretical underpinnings of chemistry were finally understood due to a series of remarkable discoveries that succeeded in probing and discovering the very nature of the internal structure of atoms. Thomson of Cambridge University discovered the electron and soon after the French scientist Becquerel as well as the couple Pierre and Marie Curie investigated the phenomenon of radioactivity.

In a series of pioneering scattering experiments Ernest Rutherford at the University of Manchester discovered the internal structure of the atom and the existence of the proton, classified and explained the different types of radioactivity and successfully transmuted the first element by bombarding nitrogen with alpha particles.

His work on atomic structure was improved on by his students, the Danish physicist Niels Bohr and Henry Moseley. The electronic theory of chemical bonds and molecular orbitals was developed by the American scientists Linus Pauling and Gilbert N. Gibbs and Svante Arrhenius in the s. Chemistry is typically divided into several major sub-disciplines. There are also several main cross-disciplinary and more specialized fields of chemistry. Other disciplines within chemistry are traditionally grouped by the type of matter being studied or the kind of study.

These include inorganic chemistry , the study of inorganic matter; organic chemistry , the study of organic carbon-based matter; biochemistry , the study of substances found in biological organisms ; physical chemistry , the study of chemical processes using physical concepts such as thermodynamics and quantum mechanics ; and analytical chemistry , the analysis of material samples to gain an understanding of their chemical composition and structure. Many more specialized disciplines have emerged in recent years, e. Other fields include agrochemistry , astrochemistry and cosmochemistry , atmospheric chemistry , chemical engineering , chemical biology , chemo-informatics , electrochemistry , environmental chemistry , femtochemistry , flavor chemistry , flow chemistry , geochemistry , green chemistry , histochemistry , history of chemistry , hydrogenation chemistry , immunochemistry , marine chemistry , materials science , mathematical chemistry , mechanochemistry , medicinal chemistry , molecular biology , molecular mechanics , nanotechnology , natural product chemistry , oenology , organometallic chemistry , petrochemistry , pharmacology , photochemistry , physical organic chemistry , phytochemistry , polymer chemistry , radiochemistry , solid-state chemistry , sonochemistry , supramolecular chemistry , surface chemistry , synthetic chemistry , thermochemistry , and many others.

The chemical industry represents an important economic activity worldwide. One knows in which miserable state this literature reached us. Collected by Byzantine scientists from the tenth century, the corpus of the Greek alchemists is a cluster of incoherent fragments, going back to all the times since the third century until the end of the Middle Ages. The study of the Greek alchemists is not very encouraging.

An even surface examination of the Greek texts shows that a very small part only was organized according to true experiments of laboratory: It is different with Jabir's alchemy. The relatively clear description of the processes and the alchemical apparatuses, the methodical classification of the substances, mark an experimental spirit which is extremely far away from the weird and odd esotericism of the Greek texts. The theory on which Jabir supports his operations is one of clearness and of an impressive unity.

In vain one would seek in the Greek texts a work as systematic as that which is presented for example in the Book of Seventy. Archived from the original on From Wikipedia, the free encyclopedia. For other uses, see Chemistry disambiguation. Avogadro's law Beer—Lambert law Boyle's law , relating pressure and volume Charles's law , relating volume and temperature Fick's laws of diffusion Gay-Lussac's law , relating pressure and temperature Le Chatelier's principle Henry's law Hess's law Law of conservation of energy leads to the important concepts of equilibrium , thermodynamics , and kinetics.

Law of conservation of mass continues to be conserved in isolated systems , even in modern physics. However, special relativity shows that due to mass—energy equivalence , whenever non-material "energy" heat, light, kinetic energy is removed from a non-isolated system, some mass will be lost with it. High energy losses result in loss of weighable amounts of mass, an important topic in nuclear chemistry. Law of definite composition , although in many systems notably biomacromolecules and minerals the ratios tend to require large numbers, and are frequently represented as a fraction.

Law of multiple proportions Raoult's law. Alchemy and Timeline of chemistry. This article relies largely or entirely on a single source. Relevant discussion may be found on the talk page. Please help improve this article by introducing citations to additional sources. A challenge for the future is to invent improved structural materials, probably composites based on resins or on ceramics, that are stable at high temperatures and easily machined.

Carbon atoms in pure form can be obtained as materials having two classic types of molecular structure: In diamond each carbon atom is linked by equivalent single bonds to four neighboring carbons. The result is a clear very hard material that is used for cutting, in saws with tiny diamonds imbedded in the blades, as tough coatings for metals, and in other industrial uses as well as in jewelry. By contrast, each carbon atom in graphite is linked to only three neighboring carbons, in a sheet, and some of the electrons are in delocalized pi orbitals that permit them to move easily along the sheets.

The extensive aromaticity of carbon sheets leads to electronic transitions with energies in the visible light region, so that graphite absorbs throughout the visible region and is a black material. In addition, the mobility of the pi electrons in graphite makes it an electrical conductor, in stark contrast to the insulating properties of diamond. A new type of structure has recently been discovered in which the sheets of graphite-like carbons are curved.

The first example, called fullerene after the geodesic domes of Buckminster Fuller , has 60 carbons in a sphere. It resembles a soccer ball with its five- and six-sided polygons in contrast to graphite, which resembles a floor tile pattern, with hexagons only. A Nobel prize was awarded in to Robert F. Kroto, and Richard E. Smalley for their discovery of fullerenes. Instead of curling into a sphere, the sheets of carbon with hexagons can also curve into tubes with diameters on the order of 1 nm often called nanotubes , tiny whiskers that are sometimes quite long.

Because of the electrical conductivity of pi electrons, these tubes are also electrically conducting, somewhat like graphite. While they are already used in research instruments to probe microscopic structures, one of the challenges is to use these new structures in miniature devices, or as building blocks for organized chemical structures. The importance of crystal form often is underappreciated. In many applications—from drugs in which bioavailability may be determined by crystal form to explosives where crystals may differ in stability and optical devices where the nonlinear optical properties required for the device are based on a particular crystalline architecture —the correct crystalline form is essential to obtaining the desired chemical and physical properties of a material.

Crystallization has long been an art rather than a science; sometimes the same substances will exhibit polymorphism and adopt different crystalline forms depending on the crystallization conditions. Crystal engineering—the prediction and control of molecular crystal structures based on the constituent molecular structures—is on the verge of becoming a science.

The current generation of computers is finally powerful. As computer capability increases, and as the sophistication of the programs used increases, it seems very probable that it will soon be possible to predict the structures of crystals. Learning to template or guide desired organization of molecules will have great utility. The scale of components in complex condensed matter often results in structures having a high surface-area-to-volume ratio. In these systems, interfacial effects can be very important.

The interfaces between vapor and condensed phases and between two condensed phases have been well studied over the past four decades. These studies have contributed to technologies from electronic materials and devices, to corrosion passivation, to heterogeneous catalysis. In recent years, the focus has broadened to include the interfaces between vapors, liquids, or solids and self-assembled structures of organic, biological, and polymeric nature. In a simple material, its surface properties are dictated by the properties of the bulk, which are not necessarily desirable. For example, we may need a bulk material for its strength but want to make a medical device—such as an artificial heart—where the surface must not cause a reaction leading to rejection or blood clotting.

This leads to the challenge of learning how to add biocompatible surface layers to materials. This challenge is not yet fully met, but interesting approaches to creating biomimetic functionality on surfaces are rapidly emerging. This field is an example of the transition of chemistry from pure materials to organized systems and materials, in this case the organization being the modification of the surface with a different material for a biofunctional purpose. The ability to modify surfaces by attaching chemicals to them has for years encouraged scientists to attempt to design surface adhesive and wetting properties.

The advent of self-assembled monolayers, including mixtures of molecules in a monolayer, has led to more detailed control and understanding of surface adhesion and wetting. This capability has been extended with the use of novel monolayers to alter liquid-crystalline anchoring processes, surface friction, and biocompatibility. Important applications of this approach have arisen in microfluidics and liquid crystalline displays. Work pioneered by Nuzzo and Allara at Bell Laboratories in the early s with thiol self-assembled monolayers on gold has led to a great deal of research, much of which has been revolutionary.

Thus the study of surfaces has emerged as an important focus in the chemical sciences, and the relationship between surfaces of small systems and their performance has emerged as a major technological issue.

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Flow in microfluidic systems—for example, in micromechanical systems with potential problems of stiction sticking and adhesion and for chemistry on gene chips—depends on the properties of system surfaces. Complex heterogeneous phases with high surface areas—suspensions of colloids and liquid crystals—have developed substantial.

In certain size ranges, we have seen new and scientifically engaging phenomena, such as electron tunneling through nanometer-thick insulators and diffraction of light in photonic band-gap crystals. New tools and systems—from scanning tunneling microscope and atomic force microscope STM and AFM to self-assembled monolayers and carbon nanotubes—have fundamentally changed our ability to characterize and prepare these complex systems.

Finally, microelectronics—complex systems of small functional components fabricated in silicon and silicon dioxide, and other materials—have become so important that we must develop the science and technology relevant to future systems of small components, whether based on microelectronics or other technologies. The microelectronics industry is entirely based on chemical processing, using such techniques as chemical vapor deposition CVD , plasma processing, etching, and electroless deposition.

As the analytical, synthetic, and physical characterization techniques of the chemical sciences have advanced, the scale of material control moves to smaller sizes. Nanoscience is the examination of objects—particles, liquid droplets, crystals, fibers—with sizes that are larger than molecules but smaller than structures commonly prepared by photolithographic microfabrication. The definition of nanomaterials is neither sharp nor easy, nor need it be.

Single molecules can be considered components of nanosystems and are considered as such in fields such as molecular electronics and molecular motors. We will define somewhat arbitrarily nanoscience as the study of the preparation, characterization, and use of substances having dimensions in the range of 1 to nm.

Many types of chemical systems, such as self-assembled monolayers with only one dimension small or carbon nanotubes buckytubes with two dimensions small , are considered nanosystems. Whether there is currently a nanotechnology is a question of definition. There is, however, a range of important technologies—especially involving colloids, emulsions, polymers, ceramic and semiconductor particles, and metallic alloys—that currently exist.

But there is no question that the field of nanoscience already exists. As new tools have become available for the preparation and characterization of systems with these dimensions, the opportunities in the chemical sciences have grown enormously. There is great interest in the electrical and optical properties of materials confined within small particles known as nanoparticles. These are materials made up of clusters of atoms or molecules that are small enough to have material properties very different from the bulk.

These are key players in what is hoped to be the nanoscience revolution. There is still very active work to learn how to make nanoscale particles of defined size and composition, to measure their properties, and to understand how their special properties depend on particle size.

One vision of this revolution includes the possibility of making tiny machines that can imitate many of the processes we see in single-cell organisms, that possess much of the information content of biological systems, and that have the ability to form tiny computer components and enable the design of much faster computers. However, like truisms of the past, nanoparticles are such an unknown area of chemical materials that predictions of their possible uses will evolve and expand rapidly in the future.

Several techniques are now available for the fabrication of nanostructures. These techniques arise from four approaches, and their simultaneous applicability to a common set of targets is one of the reasons for the excitement in the field. The first set includes the classical techniques developed from microfabrication:. The characterization of simple nanostructures is now possible with remarkable detail, but is highly dependent on access to the tools of measurement science and to scanning probe microscopies. These methods have made available a set of nanostructured systems that have begun to reveal the characteristics of nanoscale matter.

The long list of discoveries in the last decade includes:. Two important conclusions have emerged in this field. First, the methods employed for microelectronics—photolithography using UV wavelengths—are unlikely to provide inexpensive access to nanostructures. In particular, chemical affinities should make it possible for tiny structures and devices to self-assemble spontaneously, an appealing idea for large-scale manufacturing. Many of the challenges of the formation and processing of new materials will be met with advances in the chemical sciences.

There are some revolutionary things happening in materials: Self-assembly and nanotechnology are advancing rapidly, but the challenge still remains to develop a means of fabrication and manufacturing.

The rapid developments in synthetic chemistry produce myriad new polymeric and composite materials. These advances are enhanced by progress in optical, micromechanical, and spectroscopic probes. The miniaturization and diversification of synthesis through biological or combinatorial approaches provide unprecedented. The approach to the future should be a holistic one, with synthetic advances moving in concert with assembly and microstructural control. Summarized below are a few of the leaps that can be viewed as important aspirations for the chemical science community.

The development of templated syntheses—of metallic, ceramic or semiconductor particles, wires using novel synthetic and self-assembling structures such as dendrimers, micelles, and nanotubes—is in its infancy. This is a prime example where synthetic advances in the creation of new lipids, surfactants, and amphiphilic polymers work together with probes of structure and function of infinitesimal wires or particles.

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New techniques such as scanning microscopy must be developed to follow the electronic and magnetic processes occurring in the small systems. Spectroscopists, microscopists, engineers, and chemists must work together at the frontiers involving techniques developed by those from disparate fields of electronics and biology. The ability to program synthetic polymers with the correct information to self-assemble, recognize analytes, or provide biological function seems fairly futuristic.

However, the close interplay between chemical composition and physical interactions makes this a possibility; new synthetic approaches involving controlled living polymerizations and biological synthetic pathways allow control of molecular composition. Additional research on the balance of physical forces driving self-assembly, recognition, field responsive behavior, and biological compatibility should be closely tied to the synthetic efforts.

New approaches in synthetic chemistry and biochemistry pave the way for tremendous advances in self-assembly. Highly controlled living polymerizations will allow the creation of ever more complex macromolecules having prescribed architectures branching, stereoregularity and chemical specificity.

The future will hold the opportunity for chemists to make molecules of size and complexity approaching protein structures—and to fold and assemble them. Then, mimicking nature becomes a question of choosing important problems and technologies needing improvement or intervention. By creating the appropriate molecules, patterning them on the appropriate surfaces, and providing them with the appropriate functions, we can think of mimicking the most chemical of senses: These analytic advances, when taken in parallel with the computational and electronics revolution, suggest the possible creation of the robots and gadgets that were previously envisioned only in science fiction.

In other words, self-assembly of molecules or nanoparticles offers the potential for construction of miniature electronic circuits that will be faster and will permit more computer power in a given space. Promising physical approaches involve soft-lithography or crystal or nanoparticle growth, but other processes doubtless will emerge as the field of nanoparticle science evolves. Chemical scientists will seek new methods of generating nanostructures with a range of materials and processes that rely on ideas common in chemistry—self-assembly, diffusion, phase-separation, catalysis, wetting—to make these structures accessible and inexpensive.

In terms of technology, it is too early to predict what will emerge from nanoscience, although it is clear—for a field as fundamental as this one—that technologies will surely emerge. In the longer term, there will be, at minimum, demonstrations of information processors having key components with nanometer dimensions perhaps made of organic or organometallic materials and probes for exploring the interior of the cell. As self-assembly and nanotechnology move from curiosities and demonstrations to more serious means of fabrication and manufacturing, the need for characterization tools, especially those that can meet the time scales for real-time processing, will grow enormously.

Improving the molecular control of addressable, switchable, or conducting molecules that have extremely high purity, selectivity, or specificity is a goal within reach in the coming decades. This will require the combination of synthetic and processing strategies, such as recognition and controlled binding, to tailor oligomeric materials with finely tuned properties.

In this field, the chemical sciences will have to interact creatively with computer science and engineering in order to turn promising molecular switching ideas into practical computer architectures. As the ability to control materials moves to molecular dimensions, the expectations for composite materials will grow. Rather than relying on incorporation of macroscopic particles or fibers as discussed above, one can hope to create important marriages between disparate materials that will allow the development of new material properties.

Combining this synthetic expertise with physical patterning, self-assembly, deposition, or quenching techniques will lead to the creation of new materials with optimal properties. Organized nanocomposite materials can be important for photonic band gap materials as well as membranes and catalysts with high selectivity. The connection between biological function and a useful electrical signal is the capstone of sensor technology that will change medical, environmental, and personal-protection strategies in the coming decades.

The link between biology and electronics is through the chemical sciences.

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The ability to mimic nature and reliably anchor biologically active moieties to a surface is in its infancy. Here another level of complexity and functional integration are possible. Coupling the physical chemical means to manipulate interfaces with synthetic strategies inspired by nature provides powerful opportunities for gains in environmental and medical devices.

As an example, the recent understanding of virus phage packaging, combined with the ability to inject DNA into a host or a host mimic, opens the way for molecular scientists to develop new therapies and delivery strategies. Another challenge is the construction of materials with the kind of actuating response found in physiological systems such as muscle—soft materials in which a large-amplitude mechanical response could be produced in response to a small-amplitude stimulus. Capitalizing on self-assembly and nanoscience will enhance the ability to screen drugs for individual sensitivities.

Advances in drug discovery, combinatorial synthesis, and screening with sensors that have the ability to detect multitudes of specific genetic matches—marrying microelectronics and self-assembly—are expected to be near-term breakthroughs. The processing of materials through self-assembly will also have to meet several kinds of challenges that arise from scaling up in physical size and speed, and in complex shapes.

Little has been done with complex shapes and nonplanar surfaces. Can processes that work on glass slides or mica or 4-inch silicon wafers be scaled up to very large surface areas, such as continuously moving webs of paper, film, or tape, or surfaces of tubular biomaterials? Processing speed presents different challenges. Since self-assembly is a process that moves down a free energy gradient, there is a predetermined end point; but it is not known how to anticipate its speed.

Study of the kinetics and dynamics of self-assembly processes will be necessary to bring this field to a level comparable to traditional methods of synthetic chemistry and chemical engineering. Few studies of kinetics of assembly processes have been pursued, in part because following the assembly process presents analytical difficulties. Practical processing rates will certainly have to be much faster than those of typical current research laboratory practice.

The free energy landscapes along the paths toward self-assembled products are not fully explored. Local minima and metastable states lurk but are uncharted, and it is often not appreciated when they are occupied or when they are trapping the process far from the desired equilibrium state.

The challenges of kinetics and of metastable states raise the question of catalysis and whether routes to assist, accelerate, and guide self-assembly processes can be developed. Self-assembly processes in nature are sometimes catalyzed by enzymes. Zeolites are, in many ways, the inorganic counterparts of enzymes, with their ability to selectively bind other substances and perform catalysis. Can templates or catalysts be effective in increasing rates and reducing defects in a wide range of nanostructured materials? One of the most general forms of the surface modification of materials is painting.

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We have become used to the idea that paints, while serving their important function of preventing corrosion and water damage, need to be renewed on a regular basis, with a significant cost in labor and materials. One less glamorous challenge that could make a significant contribution to modern life is the invention of long-lasting paint, perhaps year paint.

In addition, it would also be desirable that this long-lasting paint be easily cleaned, perhaps simply by natural rain, and that it have a mechanism to repair damage to itself. We are used to the idea that our body can repair wounds; it is an important challenge to devise methods by which synthetic materials would also have this wound-healing ability.

As one approach, the wound might expose pools of monomer that could spontaneously fill the void and solidify. Other challenges facing materials scientists have to do with the environment. We have traditionally made materials that are as stable as possible, so they will last a long time and not need to be replaced. This longevity has the undesirable consequences of creating waste that requires significant energy to process, or else it clutters the landscape when discarded.

As one approach, chemical scientists and engineers need to focus on recycling and materials that can be easily re-. Another approach is to produce materials that undergo rapid degradation into invisible and harmless substances. Some progress has been made by incorporating ketone groups into polyethylene so that sunlight will break chemical bonds and cause the polymer to disintegrate into tiny particles. However, these materials are not yet economically attractive, and more efforts of this kind are needed.

This is part of the general need, discussed in Chapter 9 , to make materials such as insecticides or refrigerants that will degrade in the environment rather than cause problems with bird life or with the ozone layer in the stratosphere. In addition, as the world demand for synthetic materials grows, new renewable resources for chemical feed stocks must be sought, and we must reconsider our current infatuation with burning the petroleum reserves that are important feedstocks as discussed also in Chapter Zero-effluent processing plants also need to be developed.

There are innumerable opportunities for advanced chemical processing of materials to create micro- and nanodevices for environmental and ecological monitoring.

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Another challenge is to develop methods to replace the volatile organic solvents that are used in many industrial procedures. One choice is water as a solvent; it is easily repurified, and has a harmless vapor. Another choice is supercritical carbon dioxide, a good solvent for many organic substances.

IP-адрес данного ресурса заблокирован в соответствии с действующим законодательством.

It is not as innocuous as is water, but carbon dioxide can be easily recovered and reused. It is currently used to remove caffeine from coffee, and is being developed as a dry-cleaning solvent to replace organic solvents Chapter 9. For self-assembled macromolecular structures, these simulations can be approached from the atomic-molecular scale through the use of molecular dynamics or finite element analysis. Chapter 6 discusses opportunities in computational chemical science and computational materials science.

Molecular dynamics simulations are capable of addressing the self-assembly process at a rudimentary, but often impressive, level. These calculations can be used to study the secondary structure and some tertiary structure of large complex molecules. Present computers and codes can handle massive calculations but cannot eliminate concerns that boundary conditions may affect the result. Eventually, continued improvements in computer hardware will provide this added capacity in serial computers; development of parallel computer codes is likely to accomplish the goal more quickly.

In addition, the development of realistic, time-efficient potentials will accelerate the useful application of dynamic simulation to the self-assembly process. In addition, principles are needed to guide the selec-. Molecular calculations provide approaches to supramolecular structure and to the dynamics of self-assembly by extending atomic-molecular physics. Alternatively, the tools of finite element analysis can be used to approach the simulation of self-assembled film properties. The voxel 4 size in finite element analysis needs be small compared to significant variation in structure-property relationships; for self-assembled structures, this implies use of voxels of nanometer dimensions.

However, the continuum constitutive relationships utilized for macroscopic-system calculations will be difficult to extend at this scale because nanostructure properties are expected to differ from microstructural properties. In addition, in structures with a high density of boundaries such as thin multilayer films , poorly understood boundary conditions may contribute to inaccuracies. Image analysis is an important aspect of many areas of science and engineering, and imaging will play an important role in characterizing self-assembled structures as well as in on-line process control.

Development of effective noise identification and suppression, contrast enhancements, visualization, pattern recognition, and correlation algorithms should be co-opted where possible and adapted to the analysis of self-assembled structures. Models of the self-assembly process also will be important. Because self-assembled structures can be diverse, those models are likely to be highly complex. Sensitivity analysis can be an important approach to the identification and control of critical parameters.

An area of great promise for the future is that of materials for which properties change in response to external influences. The most prominent is giant magnetoresistive GMR materials—materials for which the electrical conductivity can change by a few percent under the application of an external magnetic field. GMR materials moved from a laboratory curiosity to the dominant technology in computer memories within a decade—a startling example of how a new material can completely change a major industry. The invention of new materials has been an area in which the United States has played a central role; the current emphasis on focused, shorter-term projects has, however, made it very difficult to support a lively activity in new materials, which by definition are far from a final product.

In all but the last case, these systems involve. A voxel is a volume-pixel. While a pixel is a two-dimensional point that has the attributes of height and width, a voxel is a three-dimensional point with the attributes of height, width, and depth. The area of complex condensed matter depends crucially on the availability of appropriate tools for both fabrication and characterization. They are shared-use facilities, but they must be local to the user group—travel to distance facilities for routine measurements is not practical.

Simulations in this area also require access to high-level computational capabilities. By definition, simulations involve both large numbers of atoms and dynamic behavior; both consume large numbers of CPU cycles. Because the field is so demanding on computer time, analytical theory is very important, even if it yields only approximate solutions.

Many of the tools required for the nanoscience revolution in materials involve sophisticated experiments requiring leadership, training, and infrastructure. User facilities such as high-resolution electron microscopes, synchrotrons and NMR facilities need to be easily accessible and provide adequate support for efficient experimentation. The nanometer- to micrometer-scale dimensions of supramolecular assemblies present many challenges to rigorous compositional and structural characterization.

Development of adequate structure-property relationships for these complex hierarchical systems will require improved measurement methods and techniques. The following areas constitute critical thrusts in instrument development. Many techniques ideally suited for nanostructure characterization unfortunately depend also on the substrate properties.

For example, the reflectivity and conductivity of a substrate play an important role in the successful execution of the instrumental method. Feedback provided by on-line monitoring of self-assembling processes will play an increasingly important role in controlling the microscopic and macroscopic architecture of molecular assemblies. Successful adaptation of char-. The revolution in microscopic identification and control provides new opportunities for chemists and chemical engineers. Promising routes to achieve this goal include the use of optical fibers in spectroscopic methods and the development of MEMS-based analytical instrumentation.

Order and polydispersity are key parameters that characterize many self-assembled systems. However, accurate measurement of particle sizes in concentrated solution-phase systems, and determination of crystallinity for thin-film systems, remain problematic. While inverse methods such as scattering and diffraction provide measures of these properties, often the physical information derived from such data is ambiguous and model dependent.

Hence development of improved theory and data analysis methods for extracting real-space information from inverse methods is a priority. Use of diverse techniques provides significant structural information in dispersed and thin-film systems. If significant advances in source intensities e. Since the experimental and theoretical frameworks for these techniques are well established, extension to smaller length scales should be straightforward.

The already critical need for molecular-scale compositional mapping will increase as more complex structures are assembled. Currently, electron microscopy, scanning probe microscopy SPM and fluorescence resonance energy transfer FRET are the only methods that routinely provide nanometer resolution. In contrast to the mature instrumental techniques discussed above, a hitherto nonexistent class of techniques will require substantial development effort. The new instruments will be capable of measuring the thermal e.

Materials science and engineering is inseparable from chemistry and chemical engineering. The importance of materials is illustrated by the effects they have on the quality of human life—underscored by the way our society uses new.

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