Workshop on “Soft Matter: from Fundamentals to Functionality”
Session Chair: Sathish K. Sukumaran
13:30 – 14:10

Unentangled Polymers under Fast Sear Flow: a Simulation Study
Jun-ichi Takimoto
Yamagata University, Yonezawa, Japan

14:10 – 14:50

Nonlinear modification of the Rouse model: chain volumeconservation & anisotropic friction reduction
Youngdon Kwon
Sungkyunkwan University, Suwon, Republic of Korea

14:50 – 15:30

Nonlinear Stress Relaxation of End-Associative Star Chain
Hiroshi Watanabe
Changchun Institute of Applied Chemistry, Changchun, China
Kyoto University, Kyoto, Japan

15:30 – 15:50

Short BreakSession Chair: Jun-ichi Takimoto

15:50 – 16:30

Stable Photo-active Layer of Organic Solar Cell Prepared by
Sequential Solution Deposition
Kyungkon Kim
Ewha Womans University, Seoul, Republic of Korea

16:30 – 17:10

Using swelling of polymer thin films to investigate the tightly boundlayer at a polymer/substrate interface
Sathish K. Sukumaran
Yamagata University, Yonezawa, Japan

Date: 2024, February 19 (Monday)
Venue: Room 406, Research Center for Green Materials and Advanced Processing (GMAP)
Yamagata University, Yonezawa

Organizers:
Sathish K. Sukumaran
Keiko Takeda
Research Center for Green Materials and Advanced Processing (GMAP)
Yamagata University

Unentangled Polymers under Fast Sear Flow: a Simulation Study
Jun-ichi Takimoto and Sathish K. Sukumaran
Graduate School of Organic Materials Science , Yamagata University, Yonezawa, Japan
Presenting author: takimoto@yz.yamagata-u.ac.jp
Although the linear viscoelasticity of unentangled polymeric liquids can be describedvery well by the Rouse model, unentangled polymers do show various nonlinear
behaviors. For example, the steady elongational viscosity shows thickening and thenthinning at higher strain rate [1]. This thinning is successfully described by the “frictionreduction” model. On the other hand, the steady shear viscosity η( W§ ) decreases as W§ 1/2
at high shear rate W§ [2]. To understand the origin of this shear thinning, we are now
studying various properties of unentangled polymer chains under fast shear flow. The
main results obtained so far are:(1) If there is no excluded volume interaction among the “monomers” (or “beads”) of
the chains (for example DPD model), then there is only very weak shear thinning. (2)The Kremer-Grest (KG) model with short chain length does show the shear thinning<latexit sha1_base64="rp8eyDOR2u+9uzV/bapFh65qQ9U=">AAAB1HicZY9LT8JAFIXv4AvxVWXpxsjGBWJLDLIkYWN0g4k8EqhkOl5wQmfadKYKqV0Zt/4Ft+o/8t9YsJvC2dwv995zkuP4LlfaNH9Jbm19Y3Mrv13Y2d3bPzAOjzrKCwOGbea5XtBzqEKXS2xrrl3s+QFS4bjYdSbN+b37jIHinrzXMx9tQceSjzijOlkNjeLg0dPRYEyFoPFDdG5dVOOhUTIr5kInq2ClUIJUraHxk6SwUKDUzKVK9S3T13ZEA82Zi3FhECr0KZvQMUbNm9tQj+qZZT9BSQUqO1o0yjqoUILqp3Iy1Uw4S84ky4649EONkmWNEl/0VONUlxc0D4kLSTlrucoqdKoVq1ap3V2WGvW0Zh6O4RTOwIIraMA1tKANDGbwCV/wTTrklbyR9//XHEk9RciIfPwBRy2GEQ==</latexit><latexit sha1_base64="r2K+jz78F7W89nVDytNC/UVaako=">AAABy3icZY/LTsJAFIZP8YZ4Q126MbJxQUhrDLIkYWM0JpjIJaENmY4HnNCZTjqnClaWvoJbXftGvo0Fuyn+m/lyznwn+X0dCEO2/WMV1tY3NreK26Wd3b39g/LhUdeEccSxw8MgjPo+MxgIhR0SFGBfR8ikH2DPn7QW+94zRkaE6oFmGj3JxkqMBGeUjlz3MaTEHTMp2XxYrtg1e5nT/+BkUIEs7WH5O9V5LFERD5gxA8fW5CUsIsEDnJfc2KBmfMLGmLRubmMaNXLDQYqKSTResiySN5g0ktFTNX3NTPorZnrLS4TSMaHieVHhC00Jp1Rd0uLIvJSWc1ar/IfuRc2p1+r3l5VmI6tZhBM4g3Nw4AqacA1t6AAHDR/wCV/WnWWsV+vt72vBypxjyMV6/wXTzYOF</latexit><latexit sha1_base64="r2K+jz78F7W89nVDytNC/UVaako=">AAABy3icZY/LTsJAFIZP8YZ4Q126MbJxQUhrDLIkYWM0JpjIJaENmY4HnNCZTjqnClaWvoJbXftGvo0Fuyn+m/lyznwn+X0dCEO2/WMV1tY3NreK26Wd3b39g/LhUdeEccSxw8MgjPo+MxgIhR0SFGBfR8ikH2DPn7QW+94zRkaE6oFmGj3JxkqMBGeUjlz3MaTEHTMp2XxYrtg1e5nT/+BkUIEs7WH5O9V5LFERD5gxA8fW5CUsIsEDnJfc2KBmfMLGmLRubmMaNXLDQYqKSTResiySN5g0ktFTNX3NTPorZnrLS4TSMaHieVHhC00Jp1Rd0uLIvJSWc1ar/IfuRc2p1+r3l5VmI6tZhBM4g3Nw4AqacA1t6AAHDR/wCV/WnWWsV+vt72vBypxjyMV6/wXTzYOF</latexit><latexit sha1_base64="ITPkx6YQmHcucfigJvymcDImfAc=">AAAB73icZY/LTsJAGIWneEO8VV26IbLBBGtLDLIkYWN0g4lcElrJdPzBhs60dv4qpOlbmLgzbvUR3OpL+DYW7MLi2cyX8885ybF915Go699Kbml5ZXUtv17Y2Nza3lF39zrSCwMGbea5XtCzqQTXEdBGB13o+QFQbrvQtcfN2b37AIF0PHGNUx8sTkfCGTqMYmINVM0EpGXz1sPIHFHOaXxUNP3A89Er/nVvomPjpBoP1JKu6XMV/4ORQomkag3U96SFhRwEMpdK2Td0H62IBugwF+KCGUrwKRvTEUTNi8sQh/WM2U9QUA7SiuZjswnKJad4V0leOeX2QjLpsiJH+CGCYNmggEecIEywMqdZSVxIxhmLU/5Dp6oZNa12dVpq1NOZeXJADkmZGOSMNMg5aZE2YeSJfJBP8qXcK8/Ki/L6+zWnpJl9kpHy9gM8X5FA</latexit>[( W)§ / W§ 1/2 (but within rather limited shear rate range). (3) If we allow chain crossing(by replacing the bond potential in the KG model by a simple harmonic spring) then we
can study very long but unentangled chains. This model also shows the thinning<latexit sha1_base64="ITPkx6YQmHcucfigJvymcDImfAc=">AAAB73icZY/LTsJAGIWneEO8VV26IbLBBGtLDLIkYWN0g4lcElrJdPzBhs60dv4qpOlbmLgzbvUR3OpL+DYW7MLi2cyX8885ybF915Go699Kbml5ZXUtv17Y2Nza3lF39zrSCwMGbea5XtCzqQTXEdBGB13o+QFQbrvQtcfN2b37AIF0PHGNUx8sTkfCGTqMYmINVM0EpGXz1sPIHFHOaXxUNP3A89Er/nVvomPjpBoP1JKu6XMV/4ORQomkag3U96SFhRwEMpdK2Td0H62IBugwF+KCGUrwKRvTEUTNi8sQh/WM2U9QUA7SiuZjswnKJad4V0leOeX2QjLpsiJH+CGCYNmggEecIEywMqdZSVxIxhmLU/5Dp6oZNa12dVpq1NOZeXJADkmZGOSMNMg5aZE2YeSJfJBP8qXcK8/Ki/L6+zWnpJl9kpHy9gM8X5FA</latexit>

1/2§ / W§
behavior [( W)in a wider shear rate range. (4) The chain length R under fast
1/4
shear flow behaves as ' / W§
(5) The 1st normal stress coefficient Ψ1 satisfies the2§§
1 (0) = ([( W)/[(0))
relation 1 ( W)/.
According to the generalized Rouse model [3], the result (5) indicates that thefluctuation-dissipation theorem holds even under shear flow. But to reproduce all thesimulation results for η, Ψ1 and R by the model, we need to assume that the friction<latexit sha1_base64="c0rpxNXxW1tLkLoD+7MaZRbydtM=">AAAB3XicZY9LT8JAFIVv8YX4qrrUBZGNC4KtIciShI3RDRp5JLQ203HAhs500rlVSNONiTvj1r9g3Om/8d9YkE3hbO6Xe+85yXGl7yk0jF8tt7K6tr6R3yxsbe/s7un7Bx0VRCFlbRr4QdhziWK+J1gbPfRZT4aMcNdnXXfUnN67TyxUXiDucCKZzclQeAOPEkxXjn58W7RkGEgMitZDgLE1JJyT5D42z6qJo5eMijFTcRnMOZRgrpajf6UhNOJMIPWJUn3TkGjHJESP+iwpWJFiktARGbK4eXUd4aCeWfZTFIQzZcezalkH4YoTfCynU024u+BMs+zYEzJCJmjWKNgzjpGNsTyjaUhSSMuZi1WWoXNeMWuV2k211KjPa+bhCE7gFEy4gAZcQgvaQOEFPuEbfjRHe9XetPf/15w29xxCRtrHH34sidI=</latexit><latexit sha1_base64="WHVwIAJ3qMIi2hbODgWutJ7NmGc=">AAACAHicZY9LT8JAFIWn+EJ8VV26IbKhCcGWGGRjJGFjdIOJPBJayXS84IRO23RuFdKw8b+YGDfGrX/BrS78NxbspnA28+XcOSc5tu9wibr+q2RWVtfWN7Kbua3tnd09df+gLb0wYNBinuMFXZtKcLgLLeToQNcPgArbgY49aszunUcIJPfcW5z4YAk6dPmAM4qx1VcvzKbkfaNo3nsYmUMqBJ1qJ4mpa/nzfNEEpIv3maVr2l2lrxb0sj5XfhmMBAokUbOvvsVVLBTgInOolD1D99GKaICcOTDNmaEEn7IRHULUuLoOcVBLmb0YXSpAWtF8fTpBhRQUH0rxKyfCXkjGXVbEXT9EcFk66MITjhHGWJrTrGSai8cZi1OWoV0pG9Vy9ea0UK8lM7PkiByTIjHIGamTS9IkLcLIC/ki3+RHeVZelXfl4/9rRkkyhyQl5fMPhRKVag==</latexit><latexit sha1_base64="RBatrBwBNEmJE9jnKCB5pv0oipA=">AAAB03icZY/NTsJAFIVv8Q/xr+LSjZGNC4ItMciShI3RDSYWSKCS6XjBCZ1p05kqZNKNcesruNX4Rr6NBbspnM39cu89Jzle6DOpLOvXKGxsbm3vFHdLe/sHh0fmcbkrgzii6NDAD6K+RyT6TKCjmPKxH0ZIuOdjz5u2F/feC0aSBeJBzUN0OZkINmaUqHQ1MsvDp0Dp4YRwTpJHbV/Wk5FZsWrWUmfrYGdQgUydkfmThtCYo1DUJ1IObCtUriaRYtTHpDSMJYaETskEdfv2LlbjZm45SFEQjtLVy0J5B+GSE/VcTaecc2/FmWa5mokwViho3ijwVc0UzlR1SYuQpJSWs1errEO3XrMbtcb9VaXVzGoW4RTO4QJsuIYW3EAHHKAwg0/4gm/DMbTxZrz/vxaMzHMCORkff95uhdo=</latexit>

1/2

constant does not change by the shear flow but the spring constant must grow as W§ .
This indicates that the shear thinning cannot be described simply by friction reduction
alone. Another possible model for the shear thinning is the “blob” model [2]. A simple§ / W§ 1/2 and ' / W§ 1/4, but it isapplication of the shear blob model can reproduce [( W)<latexit sha1_base64="ITPkx6YQmHcucfigJvymcDImfAc=">AAAB73icZY/LTsJAGIWneEO8VV26IbLBBGtLDLIkYWN0g4lcElrJdPzBhs60dv4qpOlbmLgzbvUR3OpL+DYW7MLi2cyX8885ybF915Go699Kbml5ZXUtv17Y2Nza3lF39zrSCwMGbea5XtCzqQTXEdBGB13o+QFQbrvQtcfN2b37AIF0PHGNUx8sTkfCGTqMYmINVM0EpGXz1sPIHFHOaXxUNP3A89Er/nVvomPjpBoP1JKu6XMV/4ORQomkag3U96SFhRwEMpdK2Td0H62IBugwF+KCGUrwKRvTEUTNi8sQh/WM2U9QUA7SiuZjswnKJad4V0leOeX2QjLpsiJH+CGCYNmggEecIEywMqdZSVxIxhmLU/5Dp6oZNa12dVpq1NOZeXJADkmZGOSMNMg5aZE2YeSJfJBP8qXcK8/Ki/L6+zWnpJl9kpHy9gM8X5FA</latexit><latexit sha1_base64="c0rpxNXxW1tLkLoD+7MaZRbydtM=">AAAB3XicZY9LT8JAFIVv8YX4qrrUBZGNC4KtIciShI3RDRp5JLQ203HAhs500rlVSNONiTvj1r9g3Om/8d9YkE3hbO6Xe+85yXGl7yk0jF8tt7K6tr6R3yxsbe/s7un7Bx0VRCFlbRr4QdhziWK+J1gbPfRZT4aMcNdnXXfUnN67TyxUXiDucCKZzclQeAOPEkxXjn58W7RkGEgMitZDgLE1JJyT5D42z6qJo5eMijFTcRnMOZRgrpajf6UhNOJMIPWJUn3TkGjHJESP+iwpWJFiktARGbK4eXUd4aCeWfZTFIQzZcezalkH4YoTfCynU024u+BMs+zYEzJCJmjWKNgzjpGNsTyjaUhSSMuZi1WWoXNeMWuV2k211KjPa+bhCE7gFEy4gAZcQgvaQOEFPuEbfjRHe9XetPf/15w29xxCRtrHH34sidI=</latexit>2§§
1 (0) = ([( W)/[(0))
very difficult to explain the relation 1 ( W)/by blob models. We
hope we get better understanding through the discussion in this Workshop.
<latexit sha1_base64="WHVwIAJ3qMIi2hbODgWutJ7NmGc=">AAACAHicZY9LT8JAFIWn+EJ8VV26IbKhCcGWGGRjJGFjdIOJPBJayXS84IRO23RuFdKw8b+YGDfGrX/BrS78NxbspnA28+XcOSc5tu9wibr+q2RWVtfWN7Kbua3tnd09df+gLb0wYNBinuMFXZtKcLgLLeToQNcPgArbgY49aszunUcIJPfcW5z4YAk6dPmAM4qx1VcvzKbkfaNo3nsYmUMqBJ1qJ4mpa/nzfNEEpIv3maVr2l2lrxb0sj5XfhmMBAokUbOvvsVVLBTgInOolD1D99GKaICcOTDNmaEEn7IRHULUuLoOcVBLmb0YXSpAWtF8fTpBhRQUH0rxKyfCXkjGXVbEXT9EcFk66MITjhHGWJrTrGSai8cZi1OWoV0pG9Vy9ea0UK8lM7PkiByTIjHIGamTS9IkLcLIC/ki3+RHeVZelXfl4/9rRkkyhyQl5fMPhRKVag==</latexit>

References[1] Matsumiya et al., Macromolecules 51 9710 (2018). [2] Colby et al., Rheol. Acta 46
569-575 (2007). [3] Watanabe et al., Macromolecules, 54, 3700 (2021)

Nonlinear modification of the Rouse model: chain volume conservation& anisotropic friction reduction
Youngdon Kwon1
1
School of Chemical Engineering, Sungkyunkwan University, Suwon, Korea
Presenting author: kwon@skku.edu
Constitutive modification of the Rouse model has been performed employing thevariation of Brownian force intensity constraining the incompressibility of molecular
chains in addition to the effects of time dependent spring constant and friction coefficient.
Assuming the normal mode-independence of stochastic forces (delta-correlation between
the eigen-modes) yields the following simple constitutive equation for the conformation
tensor 𝐜! (the case of isotropic friction):% & ('( )𝐜!(#) (𝑡̃ ) = − %! &# ('() (𝐜! (𝑡̃) − )"$#!,& ('()

𝐈+(𝑝 = 1,2, … , 𝑁).

Here 𝑡̃ is dimensionless time, 𝜃! is the p-th eigenvalue of the Rouse matrix, 𝐼!,+ (𝑡̃ ) is
the second invariant of 𝐜! , 𝐜!(#) (𝑡̃) is its upper convected time derivative and 𝐈 is theidentity tensor. 𝜅(𝑡) = 𝜅,- 𝑟. (𝑡) and 𝜁(𝑡) = 𝜁,- 𝑟/ (𝑡) are time-dependent spring andbead friction coefficients, respectively, with 𝜅,- and 𝜁,- defined as their equilibrium
values. 𝑁 is the total number of springs in one chain molecule.
Setting the number of beads per chain 𝑁 = 20 and the Weissenberg number 𝑊𝑖 = 20
in simple shear and uniaxial extensional flows we have obtained the computational results
and compared them with those of the previous results1. The current modeling together
with FENE and friction reduction closely describes the previous outcome1 with all threeeffects (however, B-variation instead) into account. Therefore, this method of Brownianforce variation constraining the chain volume may play as a useful alternative, since itdoes not introduce any additional parameter to be determined. Also, the close coincidenceof the method of chain incompressibility with the previous idea of random force variation1
suggests that the B-variation suggested in the past study1 may automatically enforce
volume conservation of unentangled chains.
The anisotropy in friction reduction regarded as an indispensable complexity for the
nonlinear modification of the Rouse model is in addition considered under the constraintof chain volume conservation, and then possible way of modeling is suggested.

References[1] T. Sato, et al., Phys. Fluids. 33, 063106 (2021).

Nonlinear Stress Relaxation of End-Associative Star Chain
Yanjie Zhang,1,2 Jian Tang,1 Quan Chen,1,2 Youngdon Kwon,3 Yumi Matsumiya,4 andHiroshi Watanabe1,4
1
Changchun Institute of Applied Chemistry, Changchun 130022, China
2
University of Science and Technology of China, Hefei 230026, China
3
School of Chemical Engineering, Sungkyunkwan University, Suwon 440-746, Korea
4
Institute for Chemical Research, Kyoto University, Uji, Kyoto 611-0011, Japan
Presenting author: hiroshi@scl.kyoto-u.ac.jp

log h(g )Associative polymers exhibit rich rheological behavior that reflects competition
between the intrinsic chain dynamics and the association/dissociation kinetics. For thosepolymers having long-lived associative groups (often referred to as stickers), the slow
rheological features are governed by the sticker dissociation. Under small strains, models
treating the effect of thermal dissociation of the stickers just as an enhancement of local
friction (so-called sticky chain models [1,2]) have been successfully applied to various
associative polymers. In contrast, large strains mechanically disrupt the sticker toactivate nonlinear rheological behavior. Recently, we have incorporated the effect of thissticker disruption in the sticky bead-spring dynamics to describe nonlinear damping
behavior of linear associative chains under single-step strain [3].
The current work extends this concept of strain-induced sticker disruption (followedby rapid thermal reformation) to associative star chains having the stickers at the arm ends
to examine their nonlinear behavior under single- and double-step strain. The star chainsforming a transient network at those stickers were modelled as a simple bead-spring chain
shown in Fig.1, and the bead-spring analysis was
r5
conducted for a fast intrinsic relaxation processactivated on the sticker disruption and a slow sticky
r2
r4
relaxation process governed by the reformed (andrz
10sticker
intact) stickers. This analysis, combined with azfree energy consideration, successfully described
r3
the nonlinear damping function h(g) of model
associative chains (tetra-PEG chains) subjected toFig.1 Bead-spring star chain
the single-step strain; see Fig.2. The analysis for
Fig 1
those chains under the double-step strain revealed
bead-spring analysis
that a cascaded memory and an isochronal crosswith Es/kBT = 2.10correlation of the arm conformations, both activatedon the sticker disruption by the first strain, govern
the relaxation under the second step strain. Details
tetra-PEG aqof these results will be presented on site.
-1-1

References[1] L. Leibler et al., Macromolecules, 24, 4701
-2
-1
0
1
2
(1991).
log g[2] M. Rubinstein and A. N. Semenov,
Fig.2 Comparison of damping
Macromolecules, 31, 1386 (1998).
function of tetra-PEG transient[3] Y. Zhang et al., J. Non-Newtonian Fluid
Fig 3 finalized with confirmationof data for tetra-PEG 0.1g/cc
gel with bead-spring
analysis.
Mech., 316, 105012 (2023).

Stable Photo-active Layer of Organic Solar Cell Prepared by
Sequential Solution Deposition
Ka Yeon Ryu,1 Juhwan Lee,1 Taesuk Jun,2 BongSoo Kim,3
Du Yeol Ryu2 and Kyungkon Kim1*
1

Department of Chemistry and Nano Science, Ewha Womans University, Seoul 03760, Republic of
Korea
2

Department of Chemical and Biomolecular Engineering, Yonsei University, Seoul
03722, Republic of Korea
3
Department of Chemistry, Ulsan National Institute of Science and Technology(UNIST), Ulsan 44919, Republic of Korea
Presenting author: kimkk@ewha.ac.kr
In order to commercialize organic solar cells (OSCs), it is essential to address changes
in the optimized morphology of the photoactive layer caused by external stimuli, which
can lead to degradation. This study presents a method to enhance OSC stability byemploying the crosslinking additive 1,8-dibromooctane (DBO) and a sequential
deposition (SqD) process to construct the photoactive layer. The crosslinking additive
incorporated in the donor polymer (PTB7-Th) secures the crystalline morphology
through partial photo-crosslinking. Ellipsometry experiments verify the increase in theglass transition temperature of the crosslinked PTB7-Th. Following the removal of the
non-crosslinked polymer and residual additive by chlorobenzene, the polymer
crystallinity is further improved. The crosslinked polymer layer establishes an efficientand stable heterojunction with a non-fullerene acceptor (IEICO-4F) layer through the
SqD process. The OSC, which is based on the immobilized PTB7-Th, demonstrates
outstanding stability against both light soaking and thermal aging. [1,2]Figure 1. Sequential deposition process of cross-linked polymer donor and non-fullerene
acceptor layer

References[1] Ryu, K. Y.; Lee, J.; Jun, T.; Lee, D.; Kim, B.; Ryu, D. Y.; Kim, K., ACS Appl.
Mater. & Interfaces 2022, 14 (20), 23474-23486.
[2] Hong, M; Youn, J; Ryu, K. Y.; Shafian, S.; Kim, K, ACS Appl. Mater. &Interfaces, 2023, 15, 20151.

Using swelling of polymer thin films to investigate the tightly boundlayer at a polymer/substrate interface
Sathish K. Sukumaran1, Sonam Z. Bhutia,2, Pradipkanti D. Lairenjem3,
Dillip K. Satapathy2s1

Graduate School of Organic Materials Science, Yamagata University, Yonezawa, Japan.
Soft Materials Laboratory, Department of Physics, IIT Madras, Chennai, India.
3
Jawaharlal Nehru Centre for Advanced Scientific Research, Bengaluru, India.
Presenting author: sa.k.sukumaran@gmail.com, sathish@yz.yamagata-u.ac.jp
2

As polymer chains can strongly adsorb to an attractive surface, a tightly bound polymer
layer can exist in supported polymer thin films and polymer nanocomposites [1]. The
tightly bound layer can be up to a few tens of nanometres thick and strongly influence
the physical properties. Therefore, in situ techniques that can shed light on thecharacteristics of the tightly bound layer without unduly disturbing it are desirable.
Recently, we introduced an approach to estimate the thickness of the tightly bound layer
at a polymer/substrate interface using the swelling of polymer thin films when exposed
to solvent vapour. The approach was tested on two hydrophilic polymers chitosan [2]and poly(vinyl alcohol) (PVA) [3] using thin films of thickness several tens to several
hundred nanometres spin coated onto carefully prepared hydrophilic silicon wafers. For
the two polymers, the time dependence of the thin film thickness during swelling wasstudied using variable angle spectroscopic ellipsometry. Assuming that the tightly boundlayer cannot swell when exposed to solvent vapour, we found that a single timedependent swelling ratio could describe the swelling of all of the thin films investigated.
We also deduced that the tightly bound layer was approximately 18 nm for chitosan and
15 nm for PVA. To corroborate the aforementioned approach, the swelling of the PVA
thin films was also investigated using X-ray reflectivity. Electron density profiles
determined by modelling the X-ray reflectivity data clearly indicated that at thepolymer/substrate interface there existed a polymer layer of a slightly higher density
than the rest of the film. The thickness of this polymer layer was found to beapproximately 15 nm, consistent with the thickness of the tightly bound layer
determined using spectroscopic ellipsometry. If time permits, I will briefly comment on
the implications of the aforementioned findings for other systems where one can expect
tightly bound polymer layers at the polymer/substrate interface to play a role.
References[1] S. Napolitano, Soft Matter, 16, 5348 (2020).
[2] P. D. Lairenjam et al., Macromolecules, 54, 10931 (2021).
[3] S. Z. Bhutia et al., Soft Matter 19, 3859 (2023).