Temperature-responsive polymers diagrams

Fig. 3 (a) Application of a high performance surface treated with a stimuli-responsive polymer for separation and purification of materials, (b) Schematic diagram of the hydrophilicity and hydrophobicity changes of a thermoresponsive PNIPAAm graft surface upon temperature changes. 

Because of the ease of temperature control in a gas chromatograph, one may explore the polymer using the probe above and below various possible phase transitions, with a linear response being revealed by the retention diagram when operating under equilibrium conditions. 

Fig. 20 Thermomechanical model for covalently crosslinked SMPs. (a) Schematic diagram of the micromechanics foundation of the 3-D SMP constitutive model (1). Existence of two extreme phases in the polymer is assumed. The diagram represents a polymer in the glass tiansition state with a predominant active phase (b) In the 1-D model, the frozen fraction (pf = Lf (T) /L(T) is defined as a physical internal state variable that is related to the extent of the glass transition, (c) Frozen fraction, (j>f (T), as a function of temperature, derived from curve fitting of the modified recovery strain curve divided by the predeformation strain, (d) Prediction of the free strain recovery responses during heating for polymers predeformed at different levels. Fig. (a) and (b) reprinted with permission from ref. [92], Copyright 2005, Materials Research Society, Warrendale, PA. Fig. (c) and (d) reprinted from [71], Copyright 2006, with permission from Elsevier.

Figure 1-3 shows a schematic diagram of a dynamic IR linear dichroism (DIRLD) experiment [20-25] which provided the foundation for the 2D IR analysis of polymers. In DIRLD spectroscopy, a small-amplitude oscillatory strain (ca. 0.1% of the sample dimension) with an acoustic-range frequency is applied to a thin polymer film. The submolecular-level response of individual chemical constituents induced by the applied dynamic strain is then monitored by using a polarized IR probe as a function of deformation frequency and other variables such as temperature. The macroscopic stress response of the system may also be measured simultaneously. In short, a DIRLD experiment may be regarded as a combination of two well-established characterization techniques already used extensively for polymers dynamic mechanical analysis (DMA) [26, 27] and infrared dichroism (IRD) spectroscopy [10, 11]. 

If tests are performed at different constant strain rates or temperatures, stress-strain response similar to that shown in Fig. 3.6 is obtained for many polymers. Notice that modulus and intrinsic yield point vary with both rate and temperature. Also, the stress-strain response appears to be nonlinear even at low stress levels. However, caution on the interpretation of the information obtained from such elementary tests is suggested, as it will be shown in a later section that linearity as well as other essential mechanical properties should be deduced from isochronous stress-strain diagrams. 

---