Effect of network topology and crosslinker reactivity on microgel structure and ordering at liquid–liquid interface

Abstract

Polymer microgels synthesized in silico were studied at liquid–liquid interface via mesoscopic computer simulations and compared to microgels with ideal (diamond-like) structure.

Compression and Ordering of Hollow Microgels in Monolayers Formed at Liquid–Liquid Interfaces

“…Since the computer simulations allow us to capture insights into the monolayer outer and inner structure, it would be helpful to start with the visualization of our systems. Figure shows the side views of the microgel monolayers at different degrees of compression measured by the area per particle A p = L x × L y / N p ( N p is the total number of microgels in the monolayer): the lower the A p , the stronger the compression . The columns in Figure correspond to the different cases of the cavity size.…”

“…The resulting compression isotherms Π( A p ) are shown in Figure a. Second, we calculated the mean-ensemble lateral R r and normal R z components of the mean gyration radius (Figure b) using the following formulae , R r 2 = 1 2 N 2 ∑ i , j N false⟨ false( x i − x j false) 2 + false( y i − y j false) 2 false⟩ R z 2 = 1 2 N 2 ∑ i , j N false⟨ false( z i − z j false) 2 false⟩ …”

“…In brief, in the first regime, the microgels weakly interact with each other ( A p = 2400 r c 2 ), and thus, no order is observed; in the second regime (1800 r c 2 ≤ A p < 2400 r c 2 ), the compression induces the formation of the two-dimensional hexagonal packing where the microgels interact with each other via coronae of the dangling ends and the peripheral part of the network (the most flattened part of microgels distinguishable in the first column of Figure ). In the third regime, the mixed core–core (between less deformed parts) and corona–corona interactions are present, which decreases the hexagonal order (1300 r c 2 ≤ A p < 1800 r c 2 ). In the fourth regime, the compression fully restores microgels’ three dimensionality, and the dominance of three-dimensional core–core contacts restores the order inside the monolayers (900 r c 2 ≤ A p < 1300 r c 2 ).…”

“…It should be noted that for monolayers formed by microgels with the actual core–corona architecture, the behavior of the monolayer shows some differences. In particular, the transition from the second to fourth regime occurs due to compression-driven submerging of coronae into the water phase while the core parts remain practically undeformed. , Meanwhile, for particles with an ideal architecture, their monolayers display more uniform deformation and stronger increase in thickness upon compression. Nevertheless, the sequence of the contact regimes and their number are the same for both types of architectures .…”

Behavior of PNIPAM Microgels in Different Organic Solvents

“…Thus, not only the overall size and density of the microgel change, but also its architecture does. It is known, for example, that the ratio between the microgel corona and core sizes has a significant effect on the particle arrangement on the liquid–liquid interface [ 50 ].…”