On the elastic nature of the demixing transition of aqueous PNIPAM solutions

Philipp, Martine; Müller, Ulrich; Aleksandrova, Ralitsa; Sanctuary, Roland; Müller‐Buschbaum, Peter; Krüger, Jan

doi:10.1039/c2sm26527c

Cited by 23 publications

(75 citation statements)

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“…20 In particular, the steep decrease of the c 11 (r)-curve proves that the large variations of the longitudinal modulus at T c are not at all governed by the evolution of the mass density. Thus, the important variation of the longitudinal modulus at T c is not dominated by variations of the mass density, but of the intermolecular and intramolecular 'spring constants', i.e.…”

Section: 2829mentioning

confidence: 99%

“…The demixing transition of these solutions is of the lower critical solution temperature type. 20,[28][29][30][31][32][33][34][35][36][37][38][39][40][41][42][43][44][45] The demixing temperature T c lies for both solutions between 33 and 34 C.…”

Section: B1 Materialsmentioning

confidence: 99%

“…Details about the experimental setup and the Brillouin spectroscopic investigations are given in ref. 20.…”

mentioning

confidence: 99%

“…Corresponding mechanical instabilities were reported for the ferroelastic demixing transition of poly(N-isopropylacrylamide) (PNIPAM) hydrogels and aqueous PNIPAM solutions. 3,20,28,29 At the demixing temperature T c , the homogeneous low-temperature phase separates into PNIPAM-rich and PNIPAM-poor domains. 20, In the course of this phase separation, the longitudinal modulus c 11 strongly decreases.…”

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confidence: 99%

“…Refractive indices versus temperature are given in ref. 20 for the PNIPAM solutions. As these values only slightly vary with temperature at the demixing transition, the magnitude of the wave vector is almost constant for each sample.…”

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confidence: 99%

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Immense elastic nonlinearities at the demixing transition of aqueous PNIPAM solutions

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Elastic nonlinearities are particularly relevant for soft materials because of their inherently small linear elasticity. Nonlinear elastic properties may even take over the leading role for the transformation at mechanical instabilities accompanying many phase transitions in soft matter. Because of inherent experimental difficulties, only little is known about third order (nonlinear) elastic constants within liquids, gels and polymers. Here we show that a key concept to access third order elasticity in soft materials is the determination of mode Grüneisen parameters. We report the first direct observation of third order elastic constants across mechanical instabilities accompanying the liquid-liquid demixing transition of semi-dilute aqueous poly(N-isopropylacrylamide) (PNIPAM) solutions. Immense elastic nonlinearities, leading to a strong strain-softening in the phase-separating PNIPAM solutions, are observed. Molecular mechanisms, which may be responsible for these immense elastic nonlinearities, are discussed. The importance of third order elastic constants in comparison to second order (linear) elastic constants in the demixing PNIPAM solutions evidences the need to focus more on the general role played by nonlinear elasticity at phase transitions within synthetic and biological liquids and gels. A IntroductionFor so condensed matter, knowledge about its continuum mechanics plays a decisive role in understanding the molecular cohesion and organization.1-21 When so matter is subjected to a sufficiently small static strain, the mechanical response is controlled by linear elastic, but not viscoelastic, properties.21 If liquids, gels or polymers are excited by a dynamical mechanical probe, their viscoelastic properties become relevant. This relevance increases with the complexity of the molecular structure in terms of inter-and intramolecular degrees of freedom. At sufficiently high probe frequencies, oen lying in the upper MHz or GHz regime, the mechanical relaxation processes are dynamically clamped and the mechanical response of the system is purely elastic again. Hence, for so materials the mechanical response may be of linear elastic nature when probed either statically or at sufficiently high probe frequencies. In such case, it can be described by Hooke's law, using the second order elastic constants (SOECs) provided by the linear elastic stiffness tensor of 4 th order.Of course linear elasticity only describes one aspect of the complex mechanical behaviour of so matter. The regime of linear elastic response is oen soon abandoned for so materials as the stress or strain amplitude is increased in stress-strain or dynamic mechanical experiments (e.g. ref. 4-6, 8 and 11-14). In order to quantify this nonlinear elastic response of the material within the frame of continuum mechanics, Hooke's law must be extended. Usually the consideration of third order elastic constants (TOECs), but no higher order elastic constants, is sufficient to describe the nonlinear elastic response. 21,22Because of the usually...

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Section: 2829mentioning

confidence: 99%

Section: B1 Materialsmentioning

confidence: 99%

“…Details about the experimental setup and the Brillouin spectroscopic investigations are given in ref. 20.…”

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confidence: 99%

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confidence: 99%

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Immense elastic nonlinearities at the demixing transition of aqueous PNIPAM solutions

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The Dependence of the Cloud Point, Clearing Point, and Hysteresis of Poly(N-isopropylacrylamide) on Experimental Conditions: The Need for Standardization of Thermoresponsive Transition Determinations

Osváth

Iván

2016

Macromol. Chem. Phys.

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Inappropriately, the critical solution temperature (CST) of lower CST(LCST)‐ or upper CST(UCST)‐type thermoresponsive polymers, measured by one, individual set of conditions, is considered almost exclusively as the LCST or UCST, respectively. These are correctly the minimum or maximum, respectively, of the full phase diagrams. Because the dynamic phase transition depends on the conditions, and no standardized or widely accepted process exists for CST determination, systematic investigations are carried out with the most widely investigated poly(N‐isopropylacrylamide) (PNIPAAm) to unveil the effect of data evaluation, measurement conditions on the transmittance–temperature curves, cloud point (TCP), clearing point (TCL), and heating–cooling hysteresis. The unusual dependence of the fundamental hysteresis parameters, i.e., width of hysteresis (XH) and extent of transmittance recovery (YH), on a broad range of conditions is revealed for the first time. On the basis of the findings, the inflection point of transmittance(absorbance)–temperature curves as TCP and TCL, 0.1 wt% solution, 0.2 °C min−1 heating/cooling steps with 5 min equilibration between the gradual change of temperature, 488 nm wavelength to obtain data comparable to light scattering at this wavelength, and determination of XH and YH are proposed as standard set of conditions.

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Thermoresponsive Polymeric Nanolenses Magnify the Thermal Sensitivity of Single Upconverting Nanoparticles

Rubio-Retama

Marin

et al. 2022

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Lanthanide‐based upconverting nanoparticles (UCNPs) are trustworthy workhorses in luminescent nanothermometry. The use of UCNPs‐based nanothermometers has enabled the determination of the thermal properties of cell membranes and monitoring of in vivo thermal therapies in real time. However, UCNPs boast low thermal sensitivity and brightness, which, along with the difficulty in controlling individual UCNP remotely, make them less than ideal nanothermometers at the single‐particle level. In this work, it is shown how these problems can be elegantly solved using a thermoresponsive polymeric coating. Upon decorating the surface of NaYF4:Er3+,Yb3+ UCNPs with poly(N‐isopropylacrylamide) (PNIPAM), a >10‐fold enhancement in optical forces is observed, allowing stable trapping and manipulation of a single UCNP in the physiological temperature range (20–45 °C). This optical force improvement is accompanied by a significant enhancement of the thermal sensitivity— a maximum value of 8% °C+1 at 32 °C induced by the collapse of PNIPAM. Numerical simulations reveal that the enhancement in thermal sensitivity mainly stems from the high‐refractive‐index polymeric coating that behaves as a nanolens of high numerical aperture. The results in this work demonstrate how UCNP nanothermometers can be further improved by an adequate surface decoration and open a new avenue toward highly sensitive single‐particle nanothermometry.

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On the elastic nature of the demixing transition of aqueous PNIPAM solutions

Cited by 23 publications

References 52 publications

Immense elastic nonlinearities at the demixing transition of aqueous PNIPAM solutions

Immense elastic nonlinearities at the demixing transition of aqueous PNIPAM solutions

The Dependence of the Cloud Point, Clearing Point, and Hysteresis of Poly(N-isopropylacrylamide) on Experimental Conditions: The Need for Standardization of Thermoresponsive Transition Determinations

Thermoresponsive Polymeric Nanolenses Magnify the Thermal Sensitivity of Single Upconverting Nanoparticles

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