Fabrication of anisotropic material is one of the important topics and we examined to introduce “anisotropic” nature by spreading polymer-grafted particle on the medium with polymer-reactive potential. Poly (tert-butyl methacrylate) (PtBMA) was polymerized from polystyrene latex (PSL) surface by ATRP to give PtBMA-grafted PSL (PSL-P tBMA). Particle monolayer was formed at air-water and air-acidic water interfaces and the monolayer characteristics were compared by π-A isotherm measurements, SEM observations, and contact angle measurements. π-A isotherms, in particular, indicates that the interaction between polymer chains become stronger by changing the subphase condition, which suggests that anisotropicparticle monolayer formation.
A particle at interface is a simplest system concerning interfaces and has wide variety of interests ranging from basic science to industrial process [
In this paper, we describe the fabrication of polymer-grafted particle monolayer with anisotropic features introduced at the air-aqueous medium interface. We have been studying polymer-grafted particle system at the air-water and oil-water interfaces [
Polystyrene latex with chloromethyl groups was synthesized by soap-free emulsion polymerization as previously described [
Molecular weight and polydispersity of free polymer were confirmed by GPC equipped with column oven (CTO-10A/10AC, Shimadzu, Kyoto, Japan) and refractive index detector (RI153, JASCO Corp., Tokyo, Japan). Obtained polymer-grafted particle was firstly characterized by dynamic light scattering (DLS). Time correlation function was fitted to single exponential function, and hydrodynamic diameter and high monodispersity was confirmed.
Estimation of graft density is performed by utilizing IR spectrum measurement as follows: Calibration curves for P(tBMA) and PSL was obtained respectively with 2-cyanoacetoamide as internal standard as same as previous study [
The preparation of particle monolayer was carried out as previously reported [
The characteristics of core PS particle and PSL-PtBMA are summarized in
PSL-PtBMA of well-characterized sample is applied to monolayer formation at the air/water interface.
Sample code | Dh/nm | Polydispersity |
---|---|---|
PSL | 118 | 0.050 |
Sample code | Mn | Mw/Mn | Graft density/nm−2 | Dh/nm |
---|---|---|---|---|
PSL-PtBMA | 76,000 | 1.41 | 0.113 | 144 |
former our papers, this indicates that polymer chains grafted from particles are much extended on the water surface [
SEM images of deposited monolayer by LB method at several constant surface pressuresare presented in Figures 3(a)-(c). These SEM images support the monolayer formation, not multilayer. We can see individual PSL core with separation of more than 150 nm.
In order to introduce “anisotropicity” in the particle monolayer by utilizing the nature of air-water interface, monolayer formation of PSL-tBMA is conducted on acidic aqueous solution of pH3. Partial proceeding of PtBMA hydrolysis in water subphase may occur because the hydrolysis of PtBMA into PMAA is irreversible reaction while PtBMA remains at the air side. However, the acidic condition here is milder than usual hydrolysis condition for PtBMA [
In
that the difference between the π-A isotherms are observed only below the plateau region. In addition to that, assuming the hydrolysis proceeds in some part, the interaction between PMAA (the resultant of hydrolysis of PtBMA) is enhanced little bet by the electrostatic interaction (although almost MAA is not dissociated in acidic pH range), which agrees with the tendency that surface pressure is increased at the larger occupied area.
SEM images of deposited monolayer by LB method at several constant surface pressures are presented in Figures 3(d)-(f). SEM images obtained at acidic condition shows more aggregated states than the ones at the air-water interface. The anisotropic nature of PSL-PtBMA at acidic condition would favors formation of large assembly of polymer-grafted PSL although we cannot ascertain whether the large aggregates are formed at the water surface or at the glass substrates.
We also estimate the surface property of deposited particle monolayer on substrate.
In the view of fabricating anisotropic particles monolayer, we investigated the behavior of PSL-P(t-butyl methacrylate) at the air/acidic water interface. PtBMA was polymerized from monodisperse polystyrene latex (PSL) surface by ATRP to givemonodisperse PtBMA-grafted PSL (PSL-PtBMA). PSL-PtBMA monolayer was characterized by π-A isotherms and SEM. PSL-PtBMA monolayer deposited from acidic condition shows more aggregated state on glass substrate rather than the ones deposited from pure water, however, the contact angle of the both
deposited film shows similar values.
We are greatly thankful to Prof. Kohji Yoshinaga (Professor Emeritus of Kyushu Institute of Technology) for his advice in the experiments especially for the synthesis of the samples. This work was financially supported by a grant-in-aid (No. 19750099, 24850015) from JSPS.
Mouri, E., Yamasaki, Y. and Terada, M. (2018) Tuning Polymer-Grafted Particle Monolayer Structure at the Air-Water Interface by Introducing Anisotropic Features. Journal of Materials Science and Chemical Engineering, 6, 11-18. https://doi.org/10.4236/msce.2018.61002