Aggregation Structure of Blood-compatible Polymer/Water Interfaces Based on a Simple
Impregnation Method
Kyushu University, Hisao Matsuno
1. Introduction
We have examined the density profiles of a deuterated poly(methyl methacrylate) (dPMMA) thin film on asolid substrate in non-solvents such as methanol and water along the direction normal to the interface by neutronreflectivity (NR) measurement and found that the interface is quite diffused in comparison with the pristine
surface probably due to the partial dissolution as well as swelling of segments into the water.

In addition, thesimilar experiments were made for poly(2-methoxyethyl acrylate) (PMEA)/dPMMA blends.
preferentially segregated at the outermost region in the blend film in water.

PMEA wasFurthermore, it has been revealed

that the density profile in the blend films near the water interface was insensitive to its molecular weight, whereas
the local dynamics became faster with decreasing molecular weight.

However, more simple methods for surface

coating with functional polymers compared to polymer blend technique are required in various industrial fields.
In this study, we examined a simple impregnation method combined with non-solvent sorption for PMEA coating
on various polymeric materials.

Especially, the density profiles of the PMEA-impregnate films along the depth

direction were examined by NR measurements.
2. Experiment
As a model underlying substrate, dPMMA and deuterated polystyrene (dPS) films were prepared on a quartz
block by a conventional spin-coating method from its toluene solution and they were dried in a vacuum oven at
298 K for 24 h. Then, the dPMMA films were immersed in 0.5 wt% solutions of PMEA in methanol at room
temperature for 2 h in order to impregnate the PMMA films with PMEA. In the case of dPS films, mixture ofmethanol and 1-butanol (50/50 (vol./vol.) was used as a non-solvent instead of methanol. After that, unfixed
PMEA chains to underlying dPMMA or dPS layers were rinsed by methanol and then the films were dried in avacuum oven at room temperature for 24 h. The density profiles of the PMEA-impregnate films along the depth
direction were examined by neutron reflectivity (NR) measurements.

Here, dPMMA or dPS was used toenhance the contrast of the scattering length density (b/V) difference between the two components, that is,impregnated PMEA and underlying layer.

A Teflon-made reservoir filled with H2O or D2O was mounted on thefilm. Prior to the measurement, the films were measured in air, and then aged in H2O or D2O. A beam ofneutrons with a wavelength ranging from 0.25 to 0.88 nm at a resolution of 3% was guided into the specimen
from the quartz side.

The (b/V) values of PMEA, PMMA, dPMMA, SiO2, H2O, and D2O used for thecalculation were 1.15×10‒4, 1.04×10‒4, 7.02×10‒4, 3.48×10‒4, ‒0.56×10‒4, and 6.38×10‒4 nm‒4, respectively.
3. Results
The upper trace in panel (a) of Figure 1 shows the scattering vector (qz) dependence of NR for the treated
dPMMA film in contact with D2O and H2O. The data set acquired in H2O was offset by the two decades. Opensymbols denote the experimental data and solid lines denote the calculated reflectivity on the basis of the model(b/V) profile shown in Figure 1(b). First, to simplify the fitting model, the film was divided into ideal two layerswith Gaussian roughnesses, unfortunately, however, the best fitting could not be attained on the basis of thebilayer model.
1(c).

Then, this lead to that the PMEA layer was further divided into sub-layers, as shown in Figure

Since the calculated NR curves were good accordance with the experimental data, it is most likely that the1(b/V) profiles in Figure 1(b) closely reflect the composition profile in the film along the direction normal to thesurface in H2O as well as D2O. The (b/V)i values for all PMEA sub-layers were greater in D2O than in air.

Thismeans that D2O with a higher (b/V) value infiltrated into these sub-layers. Also, once the film came in contact
with D2O, the PMEA layer (t2) became thicker from 16.6 nm to 18.7 nm.

These observations make it clear thatPMEA chains anchored onto the dPMMA film was definitely swollen by D2O. The NR measurement for thetreated dPMMA film in H2O enables us to gain access the depth profile of the composition in the film.

That is,assuming that the H2O distribution in the treated dPMMA film was the same as the D2O one in the film, thecomposition profiles of PMEA and water in the film were extracted.

Figure 1(d) shows the depth dependence ofvolume fraction for PMEA (φPMEA) and D2O (φD2O) in the dPMMA film in close proximity to the D2O interface.
It was revealed that the PMEA layer which was well swollen with D2O existed in the outermost region of thedPMMA film.

(a)

(b)
1.
2.

10‒210‒4

D2O
H2O

110‒6210‒800.51.0qz / nm‒11.
2.

1D2O
H2O26040200σ1σ11001008080606040402020φ PMEA / vol%IVIII
III

t1 1. dPMMA layerquartz

30-10σ0φ D2O / vol%t2

D2O (or H2O)
2. PMEA layer

5Film thickness / nm(d)t21-1100 80

1.5(c)
tIV
tIII
tII
tI

7(b/V) / 10−4·nm−2Reflectivity

10000102030

Depth / nm

Figure 1. (a) NR curves for the PMEA-impregnated dPMMA films acquired in D2O or H2O. Opensymbols depict the experimental data and lines are the reflectivity calculated on the basis of (b) the model(b/V) profiles of these films in D2O or H2O. For clarity, the NR data for the film in D2O are off-set by twodecades. (c) A schematic illustration of the model used for fitting. Here, ti and σi represent the layer
thickness and the Gaussian roughness, respectively. It is noted that the layer 2 (i.e. PMEA layer) was
divided into four sublayers (layers I, II, III, and IV). (d) Depth dependence of the volume fraction of PMEA
and D2O in the film in the D2O interfacial region. The x-axis denotes the depth from the D2O/polymerinterface.

Also, we have applied the same model described above for dPS film cases, however, unfortunately, goodaccordance between experimental data and fitting has not been obtained yet.

We have to reconsider the model on

the basis of further NR experiments and the surface morphology data acquired by atomic force microscopy and soon.
4. Conclusion
NR measurements revealed that PMEA chains were anchored to the dPMMA surface and the thickness of
PMEA layer was approximately 20 nm in water. Such the PMEA-impregnated PMMA film showed good
suppression ability for protein adsorption and platelet adhesion. In the future, we will report the results for dPS
film cases.

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