Bøger i Aktuelle Probleme der Polymer-Physik serien

70°C unterhalb des Einfrierbereichs wegen x < 0 instabil wird . .Ahnliche Uberlegungen The stability condition T ex' VI u > 0 is applied to experimental data of the specific volume of water, werden aufgrund von speziellen Modellvor­ sulfur, mercury and polystyrene, ex is the expansion stellungen von Gibbs und Dimarzio ent­ coefficient at constant pressure, u the isothermal wickelt, wobei die Autoren fUr T < T G eine compressibility, V the molar volume and T the ab­ Umwandlung 2. Ordnung postulieren (25). solute temperature. The existence of stability limits gives useful hints on molecular processes concerning Aus unseren Ergebnissen kann jedoch hin­ the change of particles. From the curve of the stability sichtlich einer moglichen Umwandlung keine limit it can be concluded that at atmospheric pressure Aussage gemacht werden. Das Gleichgewichts­ polystyrene becomes instabile at about 70°C below volumen von PST unterhalb der Einfrier­ the glass transition temperature concerning the for­ mation of phases infinitely near to each other. temperatur wird haufig aus der Extrapola­ tion der Fhissigkeitskurve gewonnen, dieses Literatur Verfahren ist nach diesen AusfUhrungen in 1) Gibbs, J. W., The Scientific Papers of J. W. einem groBeren Temperaturbereich anzu­ Gibbs, Vol. I, Thermodynamics, Dover reprint (1961). zweifeln. 2) Haase, R., Thermodynamik der Mischphasen In diesem Zusammenhang sei noch er­ (Berlin-Giittingen-Heidelberg 1956). 3) Chermin, H. A., Thesis, Essex (1971). wahnt, daB fUr Stoffe, die kristallisieren und 4) Grindley, T. and J. E. Lind, Jr., J. Chern.

Raum ist demnach beim System PST-Cyclo­ hexan um einen Faktor 1,44 gro13er als beim The self-diffusion coefficient of Benzene and Cyclo­ hexane in Polystyrene (PST) was investigated over a System PST-Benzol. Diesel' aus dem Verhalt­ wide temperature and conccntration range. The nis del' Steigungen ermittelte Wert stimmt measurements were carried out by the spin-echo­ recht gut mit dem aus dem Verhaltnis del' method applying the technique of time dependant and Van der-Waalsschen V olumina errechneten alternating field gradients. The data provided by the mentioned investigations Wert iiberein. were calculated according to the theory of free volume. The minimum free volume. which is needed for a site 3.5. Zur Phenylgruppenbeweglichkeit im. PST changing process, was determined on thc basis of these experimental results. The significant maximum Das Freie Volumen, das bis herab zu 70°C of the temperature dependence of thc free volume. linear mit sinkender Temperatur abnimmt, observed at 50 QC. revealed to be due to displacements steigt bei weiterer Temperaturerniedrigung of Phenyl-groups in PST. wieder an und zeigt im System PST-Benzol bei 55°C und im System PST -Cyclohexan Literatur bei 50°C ein ausgepragtes Maximum. Unter­ halb 40°C falIt das Freie Volumen 1(0, T) 1) Fnjita, H., Adv. Polymer Sci. 3, 1 (l!J(il). 2) Fujita, H .. A. Kishimoto. and K. Matsumoto, wieder proportional zur Temperatur. Die Trans. Faraday Soc. 56, 424 (1960).

that in all statistical calculations we only have derived most probable i.e. average quantities In this paper the meander model of muscle is proposed (e.g. geometries, forces) a.nd did not care about and treated quantitatively. The geometries of myosin and uninterrupted actin filaments as weIl as of the Z their fluctuations which in principle could also zone in vertebrate striated muscle are derived from be evaluated. thermodynamic equilibrium considerations. Cross­ The proposed meander model of muscle is bridges formed by the myosin projections and the actin suitable to explain active as weIl as passive meander folds are considered either to be loose or closed. Mg A TP action enables them to rearrange forces and removes, therefore, the difficulties. cyclically. The closed bridges give rise to a thermodynamic inherent in Huxleys sliding filament model. . contractive force on the actin filament. Also passive and We cannot exclude, however, that there is a active stress-strain behaviour (under isometrie condi­ small contribution to the passive elastic be­ tions) agree with experiment. haviour from elements (e.g. membranes) in Zusammenfassung parallel to the sliding filament system.

(Sonderausgabe aus Kolloid-Zeitschrift & Zeitschrift für Polymere, Band 241)

7) Kryszewski, M. and A. Szymanski, Macromol. Rev. 4D, 183 (1970). The density and the energetic situation of local­ 8) Bassler, H., Kunststoffe 62, 115 (1972). i;::ed levels at the polymer surface and bulk and their 9) Rose, A., Helv. Phys. Acta 29, 199 (1956). occupancy probability of excess electrons or defect­ 10) Many, A., Y. Goldstein and N. B. Grover electrons determine the electrostatic charging of Semiconductor Surfaces, 139 (Amsterdam 1971): polymer solids associated with the contact of met­ 11) Many, A., N. B. Grover, Y. Goldstein and E. als. Accumulation layers of excesselectrons and de­ Harnik, ]. Phys. Chern. Solids 14, ]D 5, 298 (1960). pletion layers of defectelectrons can exist near the 12) Many, A., Y. Goldstein and N. B. Grover polymer surface depending on the electrical potential Semiconductor Surfaces, 185 (Amsterdam 1971): of the contacting metal. These layers are caused by 13) Ryvktn, S. M., Photoelectric Effects in Semi­ the difference between the physical states of the poly­ conductors, 252 (New York 1964). mer surface and bulk. The energetic situation of the 14) Cholvdry, A. and C. R. Westgate, ]. Phys. D: localized levels is determined by intermolecular inter­ Appl. Phys. 7, 713 (1974). actions and therefore it depends on the state of 15) Many, A., Y. Goldstein and N. B. Grover, order of the surface and the bulk. Semiconductor Surfaces, 136 (Amsterdam 1971).