Solid state molecules polymers

In dilute solutions the molecules are in continuous motion and assume different conformations in rapid succession (random coils). In the solid state many polymers have typical conformations, such as folded chains and helical structures. In polypeptides helical structures containing two or three chains (double and triple helices, respectively) are found. 

In the case of polymer molecules the situation is much more complex. Polymers cannot be evaporated since they decompose before boiling. In the solid state a polymer is only exceptionally purely crystalline (so-called single crystals), but generally it is partially or totally amorphous. Furthermore a very high viscosity characterises the liquid state. 

Sometimes, the nanoporous platform must be surface-modified to create or enhance analyte-nanopore interactions that aid in separation of species. Recently, nanoporous membranes were modified via the adsorption of polyelectrolytes to various solid-state nanoporous membranes of different materials to realize the separation of ions. Ion mobility was altered in a hybrid bio-logical/solid-state nanoporous polymer membrane. The surfaces of nanofluidic channels can be chemically altered to mimic the packing material often found in liquid chromatography columns to separate on the basis of hydrophobicity. " Likewise, surface-modified polycarbonate membranes have been developed, which utilize hydrophobic interactions to achieve separation of similarly sized dye molecules. ... 

As in the previous editions, the Polymer Harkbook concentrates on synthetic polymers, poly(saccharides) and derivatives, and oligomers. Few data on biopolymers are included. Spectroscopic data as well as data needed by engineers and designers, such as mechanical and rheological data, are minimized, since many excellent compilations exist elsewhere. Only fimdamental constants and parameters that refer to the polymer molecule, that describe the solid state of polymer molecules, or that describe polymer solutions, were compiled. Constants that depend on processing conditions or on sample history were not emphasized, as they can be found in existing plastics handbooks and encyclopedias. 

Frisch FI L and Stern S A 1983 Diffusion of small molecules in polymers Crit. Rev. Solid State Mater. Sc/. 11 123... 

The aim of this chapter is to give a state-of-the-art report on the plastic solar cells based on conjugated polymers. Results from other organic solar cells like pristine fullerene cells [7, 8], dye-sensitized liquid electrolyte [9], or solid state polymer electrolyte cells [10], pure dye cells [11, 12], or small molecule cells [13], mostly based on heterojunctions between phthaocyanines and perylenes [14], will not be discussed. Extensive literature exists on the fabrication of solar cells based on small molecular dyes with donor-acceptor systems (see for example [2, 3] and references therein). 

In contrast to the solid state concepts presented above, Ioannidis et al. [90] describe the organic materials as amorphous molecules. This model is suitable to fit 1/V characteristics of LEDs based on Alq3 and PPVs with a low mobility (j.ik 1CT, h cm2 V 1 s l). Essentially, they found that the current flow through these materials can be attributed to the increase in the mobility (sec Eq. (9.18)) with the applied voltage, which has been observed for many conjugated polymers [91 ]. In the case that the mobility exponentially increases with the electric field, the current flow raids ... 

The main chain of dendronized polymers, due to die large size of the mon-odendrons, is usually forced to take a stretched shape thus the whole molecule exists as a rigid rod architecture both in solution and in the solid state.32d Depending on the backbone stiffness, the degree of monodendron coverage, and the size of die monodendron, the architecture of these macromolecules is no longer a sphere but a cylinder this dictates die properties of the dendronized polymers. 

Another type of gel expands and contracts as its structure changes in response to electrical signals and is being investigated for use in artificial limbs that would respond and feel like real ones. One material being studied for use in artificial muscle contains a mixture of polymers, silicone oil (a polymer with a (O—Si—O—Si—) — backbone and hydrocarbon side chains), and salts. When exposed to an electric field, the molecules of the soft gel rearrange themselves so that the material contracts and stiffens. If struck, the stiffened material can break but, on softening, the gel is reformed. The transition between gel and solid state is therefore reversible. 

The SCF method for molecules has been extended into the Crystal Orbital (CO) method for systems with ID- or 3D- translational periodicityiMi). The CO method is in fact the band theory method of solid state theory applied in the spirit of molecular orbital methods. It is used to obtain the band structure as a means to explain the conductivity in these materials, and we have done so in our study of polyacetylene. There are however some difficulties associated with the use of the CO method to describe impurities or defects in polymers. The periodicity assumed in the CO formalism implies that impurities have the same periodicity. Thus the unit cell on which the translational periodicity is applied must be chosen carefully in such a way that the repeating impurities do not interact. In general this requirement implies that the unit cell be very large, a feature which results in extremely demanding computations and thus hinders the use of the CO method for the study of impurities. 

Rotational-echo double-resonance (REDOR)(75,79) is a new solid-state NMR technique which is sensitive to through-space carbon-nitrogen interactions between selectively 13C and 15N-enriched sites separated by up to 5A (20-22). The parameter directly measured in a REDOR experiment is the heteronuclear dipolar coupling constant DCN, which is in itself proportional to the inverse third power of the intemuclear distance, rCN. It is this dependence on (icn)3 which accounts both for REDOR s ability to accurately measure short distances and its insensitivity to longer-range interactions. As a technique which can probe, in detail, intermolecular interactions over a distance range of 5A, REDOR is well suited to studying the distribution of small selectively-labeled molecules in polymer delivery systems. 

The REDOR 13C echo spectra of two different PMA/[l-13C]Leu/[15N]Leu samples are shown in Figure 10. Signals from the enriched carboxyl carbon of leucine are sharp at all concentrations. Apparently, even at the lowest concentration, the leucine molecules are not well dispersed throughout the polymer, but instead are clustered in small, ordered, crystalline-like domains. The doubling of the carboxyl signal is also seen for pure, crystalline leucine and is attributable to the detailed packing of the leucine molecules in the solid state. 

---