A comparison between the `coil-to-globule' transition of linear chains and the “volume phase transition” of spherical microgels1Dedicated to the 80th birthday of Professor Renyuan Qian.1

Wu, Chi

doi:10.1016/s0032-3861(97)10130-6

Cited by 172 publications

(145 citation statements)

References 76 publications

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“…The transition process from the coiled to the globular state passes different intermediate stages. 13 For the dielectric measurement the heating/cooling rate was around 0.2 K min À1 which means that the system cannot reach the equilibrium state at the LCST since the heating/cooling is too fast (see Fig. 4 and discussion).…”

Section: 40mentioning

confidence: 99%

“…9,13,16 In addition different slopes for heating and cooling are observed below the LCST which is an indication that the formation and the dissolving of globules follow different time scales (see also the discussion on Fig. 5).…”

mentioning

confidence: 93%

“…11 The ''coil-to-globule'' (heating) as well as the ''globule-to-coil'' (cooling) transitions are complex processes and pass different states. 12,13 The transition is a phenomenon widely studied because it resembles certain processes occurring in biological systems, such as protein folding and native DNA packing, but it is also related to the collapse of a gel network.…”

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confidence: 99%

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Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy

2012

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Section: 40mentioning

confidence: 99%

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confidence: 93%

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confidence: 99%

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Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy

2012

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“…This is attributed to kinetic effects for instance the formation of additional hydrogen bonds in the collapsed state between different chain segments when they are overlapped which hinders the swelling process during cooling. 39,40 With increasing crosslinker content, the chain length between two crosslinking points decreases. Therefore fewer intrachain hydrogen bonds can be formed during the heating scan (collapsing), and the hysteresis becomes smaller and vanishes, respectively.…”

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confidence: 99%

The dielectric signature of poly(N-isopropylacrylamide) microgels at the volume phase transition: dependence on the crosslinking density

2013

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Temperature sensitive poly(N-isopropylacrylamide) (pNIPAM) microgels are prepared and investigated using dielectric spectroscopy in a frequency range from 10 À1 Hz to 10 6 Hz at temperatures from 15 C to 50 C. The microgels were synthesized with different crosslinker molar ratios resulting in microgels with structural differences. From the dielectric response of the pNIPAM microgels the swelling/ deswelling behaviour is monitored by both the temperature (T) and the frequency ( f ) dependence of the conductivity spectra s*(f, T). The volume phase transition (VPT) at the lower critical solution temperature (LCST) is deduced by a change in the T-dependence of the DC conductivity s 0 DC . It can be explained by a decrease in the effective charge mobility and a reduction in the effective charge number contributing to s 0 DC at T > LCST. Addressing the f-dependence of the real part of the conductivity s 0 , a pronounced frequency dependence at temperatures above the LCST can be observed whereas at temperatures below the LCST the conductivity spectra resemble that of the pure solvent (water) which is frequency independent. The f-dependence of s 0 at T > LCST is assigned to the collapse of the microgel particles. At the interfaces of the collapsed particles charge carriers are blocked and/or entrapped giving rise to Maxwell-Wagner-Sillars (MWS) polarization effects. The dependence of the MWS effect on the crosslinker amount is studied in detail and conclusions concerning the internal structure of the microgels with respect to their crosslinking density are drawn. Moreover the dielectric data are related to dynamic light scattering data. A correlation between the MWS polarization effect and the swelling/ deswelling ratio expressed by the hydrodynamic radius R h at different temperatures is established for the first time.

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“…34,35 The relatively weak EM and more specifically the radiofrequency response necessitates increased susceptibility to RF to successfully obtain amplified responsiveness. [36][37][38] An applied EM field results in a rearrangement of the charges as they tend to align with the external field. The power density dissipated due to an EM field in a material with low magnetic susceptibility is…”

Section: Rf Actuated Acoustic Materialsmentioning

confidence: 99%

Radio-frequency actuated polymer-based phononic meta-materials for control of ultrasonic waves

Walker

Wang²,

Neogi

2017

NPG Asia Mater

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Radio-frequency (RF) control of an ultrasonic phononic crystal was achieved by encapsulating it in a composite of high k-10% KF-doped BaTiO 3 dielectric nanoparticles with poly(N-isopropylacrylamide) (PNIPAm)-based hydrogel. The combination of the nanoparticles and hydrogel produced a composite with elastic properties susceptible to RF actuation. The novel acoustic meta-material enables the regulation of sound waves by electromagnetic waves, which is not possible in a conventional medium as elasto-mechanical waves, and electromagnetic waves do not directly couple. Compared with light waves, radio waves can penetrate deeper into bulk structures and enable the control of propagation of ultrasonic waves through a macroscale phononic crystal. An RF antenna emitting at 318.6 and 422.5 kHz was used to modulate the device in water and ambient air, respectively. An increased transparency of the ultrasonic wave in the material was observed due to an increase in the bandwidth of the modulated device exceeding 8 kHz with a 30-fold increase in the signal modulation at select frequencies. The radio waves induced changes in the transmission and demonstrated the control of ultrasound with applied RF. The synthetic acoustic properties in the resultant meta-material device were actively manipulated through the interaction of electromagnetic waves with the material.

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A comparison between the `coil-to-globule' transition of linear chains and the “volume phase transition” of spherical microgels1Dedicated to the 80th birthday of Professor Renyuan Qian.1

Cited by 172 publications

References 76 publications

Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy

Probing the phase transition of aqueous solutions of linear low molecular weight poly(N-isopropylacrylamide) by dielectric spectroscopy

The dielectric signature of poly(N-isopropylacrylamide) microgels at the volume phase transition: dependence on the crosslinking density

Radio-frequency actuated polymer-based phononic meta-materials for control of ultrasonic waves

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