Identification of volume phase transition of a single microgel particle using optical tweezers. (9th September 2016)

• Record Type: Journal Article
• Authors: Karthickeyan, D; Gupta, Deepak K; Tata, B V R
• Is Part Of: Journal of optics. Volume 18:Number 10(2016:Oct.)
• Publication Date: 2016-09-09
• Subjects: optical tweezers -- optical trapping -- stimuli responsive microgels -- phase transition; 87.80.Cc -- 82.70.Dd -- 82.70.Kj -- 64.70.km; Optics -- Periodicals; 535.05
• DOI: 10.1088/2040-8978/18/10/105401
• Languages: English
• ISSNs: 2040-8978

Abstract

Abstract: Poly (N-isopropyl acrylamide-co-acrylic acid) (PNIPAM-co-Aac) microgel particles are pH responsive and exhibit volume phase transition (VPT) upon variation of pH. Dynamic light scattering (DLS) is used conventionally to identify VPT and requires a dilute suspension with particle concentration ∼10 7 particles cm −3 and if particles are polydisperse in nature, DLS data interpretation is relatively difficult. Here we show that optical tweezers allow one to measure the VPT of a single microgel particle by measuring the optical trap stiffness, κ of trapped particle as a function of pH. We report here a sudden change in κ at VPT, which is shown to arise from a sudden decrease in particle diameter with a concomitant increase in the refractive index of the particle at VPT.