Correlative infrared nanospectroscopic and nanomechanical imaging of block copolymer microdomains.

Benjamin Pollard,Markus B Raschke

doi:10.3762/bjnano.7.53

Abstract

Intermolecular interactions and nanoscale phase separation govern the properties of many molecular soft-matter systems. Here, we combine infrared vibrational scattering scanning near-field optical microscopy (IR s-SNOM) with force–distance spectroscopy for simultaneous characterization of both nanoscale optical and nanomechanical molecular properties through hybrid imaging. The resulting multichannel images and correlative analysis of chemical composition, spectral IR line shape, modulus, adhesion, deformation, and dissipation acquired for a thin film of a nanophase separated block copolymer (PS-b-PMMA) reveal complex structural variations, in particular at domain interfaces, not resolved in any individual signal channel alone. These variations suggest that regions of multicomponent chemical composition, such as the interfacial mixing regions between microdomains, are correlated with high spatial heterogeneity in nanoscale material properties.

Highlights

Functional soft-matter and polymer systems often exhibit novel phenomena due to nanoscale chemical heterogeneity and the resulting intermolecular interactions
Performed most with a single-frequency source tuned to a molecular marker resonance [2], IR s-SNOM enables IR spectroscopy on the nanoscale using broadband [3,4] or tunable light sources [5]
We study a high molecular weight block copolymer of polystyrene-block-poly(methyl methacrylate) (PS-b-PMMA), with a relative chain length of 270.0-b-289.0 Mn × 103 (P4443SMMA, Polymer Source), spin-coated from a 1% w/v solution in toluene onto native-oxide silicon substrates (2 kRPM)

Summary

Introduction

Functional soft-matter and polymer systems often exhibit novel phenomena due to nanoscale chemical heterogeneity and the resulting intermolecular interactions. Infrared vibrational scattering scanning near-field optical microscopy (IR s-SNOM) provides a direct, noninvasive, label-free measure of nanoscale chemical composition by localizing the light–matter interaction via a scanning probe tip [1]. Performed most with a single-frequency source tuned to a molecular marker resonance [2], IR s-SNOM enables IR spectroscopy on the nanoscale using broadband [3,4] or tunable light sources [5]. Combined with computational imaging to analyze spectral peak position and lineshape, as well as polarization selection, s-SNOM can probe intermolecular coupling [6], polymorphism [7], molecular orientation, domain structure [8], and degrees of crystallinity.

Methods

Results

Conclusion