Block Copolymer Self Assembly during Rapid Solvent Evaporation: Insights into Cylinder Growth and Stability

Sep 21, 2026

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Solvent evaporation directs block-copolymer self-assembly, but microscopic mechanisms and how processing history and control parameters govern pattern selection remain unclear. Using dynamical field theory simulations, the study clarifies the evaporation-stage evolution. Cylinders oriented vertically are favored at modest evaporation rates and weaker segregation strengths, tied to morphology-dependent density correlations at the ordering front. The results support rational design of solvent-annealing systems.

LanguageEnglish

CategoryResearch & Report

FormatPDF

Pages5

Reading Time13 min

AccessFree to download

Abstract

Overview and motivation

Model and interactions

Evaporation kinetics and Hertz-Knudsen flux

Simulation setup and morphological trends

Dependence on evaporation rate and segregation strength

Letter [pubs.acs.org/macroletters](pubs.acs.org/macroletters) Block Copolymer Self Assembly during Rapid Solvent Evaporation: Insights into Cylinder Growth and Stability Sean P. Paradiso,† Kris T. Delaney,‡ Carlos J. García-Cervera,§ Hector D. Ceniceros,§ and Glenn H. Fredrickson *,†,‡ †Department of Chemical Engineering, ‡Materials Research Laboratory, Materials Department, and §Department of Mathematics, University of California, Santa Barbara, California 93016, United States *S Supporting Information | ABSTRACT: Solvent evaporation has proven to be a remarkably successful tool for directing self-assembly in block copolymers, yet the microscopic mechanisms, processing history dependence and macroscopic control parameters inﬂuencing pattern selection remain poorly understood. Here, we leverage dynamical ﬁeld theory simulations to clarify how copolymer self-assembly proceeds during evaporation. We ﬁnd that cylinders in the vertical orientation tend to form under modest evaporation rates and relatively weak segregation strengths, and link this behavior to nontrivial, morphology-dependent density correlations present at the ordering front. | | | --- | --- | | | | Block copolymers have emerged over the past decade as a versatile platform for a wide range of thin-ﬁlm technologies including nanoﬁltration,1 optical coatings,2 and lithography.3 For applications that require patterning nanoscopic pores, such as separation membranes or lithographic masks, cylinder morphologies oriented vertically (C⊥) are required, but often not thermodynamically preferred. In order to meet these design constraints, researchers have turned to solvent-mediated annealing techniques, which oﬀer a number of advantages over conventional thermal annealing, including enhanced defect annihilation kinetics and additional interaction handles for tuning ﬁlm morphology.4−10 Still, with the notable exception of works by Osuji and others deploying pressuredriven solvent ﬂows,11,12 these techniques can, at best, only mitigate the thermodynamic driving force for forming lying- down cylinders ( C ∥ ), orientation. In their not actively promote a vertical seminal work, Kim and Libera 13 demonstrated that more direct inﬂuence over morphology orientation can be achieved by controlling the rate at which solvent-cast ﬁlms are dried. In their experiments, the equilibrium C ∥ rphology was observed for modest eswelling rates ( 0.001 mm/min), while increasing to 0.003 mm/min led to an unexpected reorientation to C⊥ persisting over a large area. In the wake of this and subsequent work,7,9 an expectation has developed that rapid evaporation actively drives the growth of vertical cylinders, 14 which an earlier theoretical treatment appears to support.15 More recent evidence, however, indicates that the degree of perpendicular ordering weakens with increasing evaporation rate beyond a certain threshold.16 After over a decade of experience, there is still no consistent picture of evaporation-induced ordering in block copolymer systems. While many factors conspire to obscure the fundamental forces involved in this process, slow development is attributed in large part to the black box nature of self-assembly during the solvent removal step.17 Here, we use a dynamical extension of self-consistent ﬁeld theory simulations (SI for details) to describe this process and provide a rational basis for designing solvent annealing systems. Our model describes the self-assembly dynamics of monodisperse diblock copolymers, comprised of chemically distinct A and B type segments in a good, neutral solvent, S. Polymers in the theory chains with total length are described by continuous Gaussian N, unperturbed coil radius Rg ∼ √N, and minority A-block fraction fA. All species in the model interact through local, Flory-type contact potentials with strength χABN, χASN, and χBSN for polymer−polymer and polymer−solvent interactions, respectively. 18−20 When a droplet o

FAQs

What method is used to study copolymer self-assembly during evaporation?

The work leverages dynamical field theory simulations to model the self-assembly process while solvent evaporates.

Under what conditions do vertical cylinders tend to form?

Vertical cylinders are predicted for modest evaporation rates combined with relatively weak segregation strengths.

What factor links cylinder formation to microscopic behavior?

The study connects cylinder orientation to morphology-dependent density correlations present at the ordering front during evaporation.

Sep 21, 2026

Uploaded by Putri