Amorphous relaxed structure

The problems associated with freeze drying of peptides and proteins for therapeutic use have also received calorimetric attention recently - particularly, attempts to understand and interpret the dynamics of amorphous solids. Structural relaxation time is a measure of molecular mobility involved in enthalpy relaxation and thus is a measure of the dynamics of amorphous (glassy) solids. These dynamics are important in interpretation of the physicochemical properties and reactivities of drugs in amorphous formulations. The authors conclude that microcalorimetry may provide data useful for rational development of stable peptide and protein formulations and for control of their processing . 

Hence, the cluster model of polymers amorphous state structure allows to identify structural relaxation mechanisms in them. In the case of glassy loosely packed matrix relaxation process is realized by conformational reorganizations in this structural component (mechanism I) and in the case of its devitrification - clusters mutual motions (mechanism II). 

Kozlov, G. V, Beloshenko, V. A., Shogenov, V. N. (1999). An Amorphous Polymers Structural Relaxation Description within the Framewoiks of Cluster model Fiziko-Khi-micheskaya Mechanika Materialov, 35(5), 105-108. 

As it is known [2, 12], within the frameworks of cluster model the elasticity modulus E value is defined by stiffness of amorphous polymers structure both components local order domains (clusters) and loosely packed matrix. In Fig. 13.3, the dependences E(v J are adduced, obtained for tensile tests three types with constant strain rate, with strain discontinuous change and on stress relaxation. As one can see, the dependences E(yJ are approximated by three parallel straight lines, cutting on the axis E loosely packed matrix elasticity modulus E different values. The greatest value E is obtained in tensile tests with constant strain rate, the least one - at strain discontinuous change and in tests on stress relaxation E = 0 [1]. 

The authors of Ref. [21] supposed, that in orientational drawing process of poly(metyl methacrylate) (PMMA) the following structure changes occur the transition to more equilibrium structure owing to molecular package improvement and internal stresses relaxation. The quantitative structural model absence not allows the authors of Ref [21] to give direct proofs of their suppositions. In Ref [22] such treatment was fulfilled on the example of extruded amorphous polyarylates DV and DF-10 with the cluster model of polymers amorphous state structure using [12, 23],... 

Figure 9.10 Schematic representations of change in modulus E with temperature on the Takayanagi model for (a) the and (b) the situations corresponding to Eo and Ego respectively. Calculations assume amorphous relaxation at temperature T(oca) and crystalline relaxation at temperature T(ad and (c) shows combined results. C, crystalline phase A, amorphous phase. (Reproduced from Takayanagi, M., Imada, I. and Kajiyama, T. (1966) Mechanical properties and fine structure of drawn polymers. ). Polym. Sci. PoL Sym., 15, 263. Copyright (1966) John Wiley Sons, Ltd.)...

The relaxation modulus (or any other viscoelastic function) thus obtained is a mean s of characterizing a material. In fact relaxation spectra have been found very useful in understanding molecular motions of plastics. Much of the relation between the molecular structure and the overall behavior of amorphous plastics is now known. 

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