Synthesis and characterization of PNIPAM/PS core/shell particles

Zhang, Li; Daniels, Eric S.; Dimonie, Victoria L.; Klein, A.

doi:10.1002/app.31508

Cited by 19 publications

(24 citation statements)

References 30 publications

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“…8 In the literature the transition temperature is therefore also called volume phase transition temperature (VPTT). 5 The volume phase transition (VPT) is a reversible process. The macroscopic driving force for the volume change (collapse) is related to the competition between mainly two molecular effects, hydrogen bonding and hydrophobic interaction.…”

Section: 7mentioning

confidence: 99%

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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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Section: 7mentioning

confidence: 99%

“…[1][2][3][4][5] Poly(N-isopropylacrylamide) (pNIPAM) is one of the most widely studied thermosensitive materials with a lower critical solution temperature (LCST) at around 32 C in aqueous media.…”

Section: Introductionmentioning

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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“…The simplest way to further confirm that the PS shell formation results from the heterocoagulation process is to mix PS latex particles with PNIPAM latex particles in various ratios. Therefore, PS latex particles shown in Figure (L‐PNIPAM 30) were utilized in the mixing experiment while PNIPAM latex particles were synthesized individually by following the synthesis method described in the literature . The corresponding particle sizes were measured by CHDF as shown in Figure .…”

Section: Resultsmentioning

confidence: 99%

“…The detailed description of the procedure used to prepare PNIPAM particles and PNIPAM/PS core/shell particles was shown previously …”

Section: Methodsmentioning

confidence: 99%

“…In our previous paper, two different polymerization methods were used to prepare PNIPAM/PS core/shell particles, either above or below the volume phase transition temperature (VPPT) using either a multi‐stage or semi‐batch polymerization process. In both processes, uniform “raspberry” structures were obtained in which polystyrene formed small domains on the surface of the PNIPAM particles.…”

Section: Introductionmentioning

confidence: 99%

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Mechanism for the formation of PNIPAM/PS core/shell particles

Zhang

Daniels

Dimonie

et al. 2013

J of Applied Polymer Sci

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A multi-stage polymerization method was previously used to prepare PNIPAM/PS core/shell particles that exhibited uniform "raspberry-like" structures. In this current study, this polymerization process was carefully investigated in order to elucidate the PS (polystyrene) shell formation mechanism. The results indicated that the "raspberry" structure is due to heterocoagulation of polystyrene domains onto PNIPAM (poly(N-isopropylacrylamide)) particle surfaces. Different sizes and numbers of the PS domains can be obtained by varying the styrene feed rate. It was also found that linear PNIPAM may increase the compatibility between PNIPAM and PS polymers. In addition, this heterocoagulation mechanism for forming structured particles was successfully applied to a PNI-PAM and Ludox V R colloidal silica nanoparticle system where a core/shell structure was also obtained. V C 2013 Wiley Periodicals, Inc. J.Appl. Polym. Sci. 2014, 131, 40124.

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Temperature effect on mechanical strength and frictional properties of polytetrafluoroethylene‐based core‐shell nanocomposites

Bian

Zhang

et al. 2020

J of Applied Polymer Sci

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Polytetrafluoroethylene (PTFE) has shown an outstanding lubricity as a solid lubricant, but its application is limited due to its low-mechanical strength and high-wear rate. In this study, core-shell nanoparticles were synthesized using PTFE as the core and polymethylmethacrylate (PMMA) as the shell. The formed core-shell nanocomposites by leveraging the core-shell nanoparticles as basic structural units exhibit remarkable enhancement on uniformity, tensile strength, and wear resistance, compared to mechanically mixed composites with the same composition. Our experiments demonstrated the following results: (1) Owing to the excellent uniformity, the maximum tensile strength of core-shell nanocomposites was 62 MPa, three times higher than that of mechanically mixed composites. (2) The composite matrix formed by PMMA shell had better reinforcement and protection effect on inner PTFE phase, resulting in a reduced wear rate of 0.3 × 10 −5 mm 3 /(N m), one order of magnitude lower than that of mechanically mixed composites. (3) The friction coefficient and interfacial mechanical properties of the core-shell nanocomposites at different temperatures have been systematically studied to get insights into lubrication mechanisms. It is proved that the temperature can decrease the modulus and increase the interfacial adhesion as well as the loss tangent of the core-shell nanocomposites, thus affecting the lubrication properties in multiple ways.

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Synthesis and characterization of PNIPAM/PS core/shell particles

Cited by 19 publications

References 30 publications

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

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

Mechanism for the formation of PNIPAM/PS core/shell particles

Temperature effect on mechanical strength and frictional properties of polytetrafluoroethylene‐based core‐shell nanocomposites

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