Temperature switches response time

Section 7.3.1.2. Switching response times were shown to be shorter for polymers of lower DP but the variation levelled off at DP 30. Each polymer switched most quickly at a temperature near the upper end of its S phase, and switching times were around 4-15 ms—much faster than those associated with nematic comb LCPs. 

Ferroelectric siloxane combs have also been prepared (cf. Ref. 25), and some examples are shown in Fig. 7.29. Polymers of type I (n = 6,10,11) all gave room-temperature S mesophases while polymers of type II (n = 6, 8) gave no S phase at any temperature, highlighting the importance of the constitution of the spacer chain.The length of the spacer affected both the detailed transition temperatures (cf. Table 7.14) and the switching response times, which decreased as n increased and which were well below 1 s at appropriate applied voltages. 

Typical response times of SmC FLCPs are of the order of a few milliseconds to a few hundred milliseconds, depending (through the viscosity) on the temperature, the chemical nature of the polymer backbone, and the molecular weight of the polymer. The switching time T increases with the molecular weight and decreases as the temperature increases. On the other hand, the response time measured at the same reduced... 

Electroclinic behavior has been recognized in few SmA LCPs [77] and response times in the sub-millisecond range have been observed. But, surprisingly, the SmC X phase of polyacrylate V-11 exhibits an electroclinic switching process with a short response time (200 p s) that is changed into a ferroelectric one as the temperature is raised. Moreover, the electroclinic-ferroelectric transition is shifted towards lower temperatures when the voltage is increased (Fig. 20). 

Similar to the phase transition from nematic to isotropic phase induced by azobenzene molecules, the trans-cis isomerization also destabilize the SmC phase composed of calamitic mesogens and lower the Curie point, which is a transition temperature where the SmC will transform from ferroelectric to non-ferroelectric. Some examples have been reported with an early demonstration by Ikeda et al. [130-135]. For example, a photoresponsive SmC was formulated by doping 3 mol % of 4,4 -disubstituted azobenzene 29 into a FLC host 27 and the UV irradiation at 260 nm resulted in the lowering of Curie point and the coercive force Ec required to switch the SSFLC due to the destabilization of bent shape cis isomers [130] (Fig. 5.23). When the electric field was close to Ec before irradiation, the flip of polarization of SmC was achieved. It is noteworthy that its response time 500 ps is much faster than normally observed for photochemical N-I phase transitions [131]. 

Over the last two decades research has concentrated on the production of low molar mass liquid crystal materials with electro-optical properties suitable for use at ambient temperatures. Since one highly desirable property was electro-optic switching on a reasonably fast timescale (i.e. faster than the eye response time of —100 ms) and because this switching time depends on cooperative molecular reorientation, attention was focused on the synthesis of relatively small molecules of low mean viscosity of the type... 

Fig. 15.3 (a) Room-temperature phosphorescence spectra of platinum-octaethylporphyrin (PtOEP)-doped sol-gel glass under different atmospheric conditions top), ambient conditions (middle), and bottom). Excitation wavelength, 535 nm. (b) Response time, relative intensity change, and reproducibility of sensor response on switching between 100 % nitrogen (a) and 100 % oxygen (Reprinted with permission from Lee and Okura 1997, Copyright 1997 Royal Society of Chemistry)... 

We have presented here the first observation of transient molecular reorientation induced in a liquid crystal by a -switched laser pulse. The response time of molecular reorientation in the nematic phase is of the order of 10—100 psec. Although this is 10 —10 times longer than the duration of the laser pulse, transient molecular reorientation is still strong enough to yield an easily detectable phase shift in the probe beam. Residual al> sorption and subsequent very rapid radiationless conversion into heat can result in a temperature rise in the medium which decays via heat diffusion with relaxation times in the 10—200 msec range. The temperature rise also induces a refractive-index change in the medium and hence a phase shift in the probe beam. This thermal effect and the molecular reorientation are initiated simultaneously by the pulsed laser excitation. They are in general coupled... 

Miniaturization of systems for chemical analysis offers an improved efficiency with respect to sample size, response time and reagent consumption [1,2]. In microreactors, temperature control can be very important. Integrated cooling and heating has however hardly been studied. In this work we compare three possible techniques for integrated temperature control a Peltier element, a thermal switch and a fluid cycle. 

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