Thermodynamic Correlation Between Surface Carboxyl Configuration and Wettability

doi:10.7503/cjcu20250303

Abstract

Abstract:

In this study， polyacrylic acid（PAA） films were employed as a model system， and a series of PAA films with tunable water wettability was systematically prepared by varying molecular weight and curing temperature. Using attenuated total reflectance Fourier-transform infrared spectroscopy（ATR-FTIR）， the molecular configurations of surface carboxyl groups（COOH）， free carboxyl（ $C O O H f$ ） and hydrogen-bonded carboxyl（ $C O O H H B$ ）， were directly correlated with the polar component of surface energy（ $γ s, p$ ）. By decomposing the $γ s, p$ values of the PAA thin films as a sum of the contributions of $C O O H f$ and $C O O H H B$ ， the intrinsic polar component of surface energy of $C O O H H B$ （ $γ H B s, p *$ ） was quantified for the first time as 8.34 mN/m， significantly lower than that of $C O O H f$ （ $γ f s, p *$ =34 mN/m）. This result highlights that hydrogen bonding markedly reduces the $γ s, p$ ， providing a rational explanation for the relatively large water contact angle observed on PAA thin films. Furthermore， it establishes a thermodynamic basis for estimating the fraction of surface $C O O H H B$ groups（ $f H B$ ） from wettability measurements. Further extension of the model to carboxyl- terminated self-assembled monolayers（COOH-SAMs） revealed that surface COOH density（∑C^{OOH） critically regulates wetting behavior： when ∑C OOH ranges from 4.30 to 5.25 nm^-²， COOH groups predominantly exist in a free state and facilitate effective hydration layers， thereby promoting superhydrophilicity. Overall， this study not only establishes a unified thermodynamic framework linking surface COOH configurations to macroscopic wettability， but also validates its universality by extending it to COOH-SAMs systems， thereby providing a unified theoretical framework for the controllable design of hydrophilicity in various COOH-functionalized surfaces.}

Key words: Polyacrylic acid film, Hydrogen bonding, Attenuated total reflectance Fourier-transform infrared spectroscopy, Quantitative carboxyl configuration, Polar component of surface energy

CLC Number:

O647

TrendMD:

GUO Zhuohuan, WANG Dayang. Thermodynamic Correlation Between Surface Carboxyl Configuration and Wettability[J]. Chem. J. Chinese Universities, 2026, 47(1): 20250303.

Figures/Tables 6

Fig.1 AFM images of as⁃prepared H-PAA20 ℃ thin film(A), H-PAA100 ℃ thin film(B) and H-PAA170 ℃ thin film(C) with the corresponding RMS values marked, plot of the θw/a values of as⁃prepared H-PAAT, M-PAAT and L-PAAT thin films versus the curing temperature(T), in which the photos of a 2 μL droplet of water placed on the corresponding thin films are shown(D) and histograms of the values of γs,p of as⁃prepared H-PAAT, M-PAAT and L-PAAT thin films(E)

Table 1 Infrared bands of PAA thin films

Wavenumber/cm^-1	Assignment
3600—3000（broad）	O—H stretching
2930	CH₂ stretching
2500—2700（broad）	Overtones and combinations of bands near 1412 and 1238 cm^-1
	enhanced by Fermi resonance
1695—1725（strong）	C=O stretching
1526	Acid anhydride stretching
1457	CH₂ deformation
1412， 1238， 1165	C—O stretching coupled with O—H in⁃plane bending
846	C—COOH stretching

Fig.2 ATR⁃FTIR spectra of H-PAAT (A), M-PAAT (B) and L-PAAT (C) thin films in the range of 4000—400 cm-1 and the summary of the O—H stretching vibration peak intensity on the surface of H-PAAT, M-PAAT and L-PAAT thin films(D)

Fig.3 ATR⁃FTIR spectra of COOH⁃SAMs and PAA thin films in the range of 4000—2000 cm-1(A), plots of the calculated ffM,T and fHBM,T values of as⁃prepared PAA thin films versus the θw/a(B), plots of the γ(M,T)s,p values of as⁃prepared PAA thin films versus their ffM,T and fHBM,T values(C), and plots of the ffM,T-1 values of as⁃prepared COOH⁃SAMs and PAA thin films versus their γM,Ts,p-γfs,p* values(D)

Table 2 Summary of the values of AHBM,T,fHBM,T,ffM,T and γM,Ts,p of as-prepared COOH⁃SAMs and PAA thin films

COOH Surface	COOH⁃SAMs	$H - P A A 20 ℃$	$M - P A A 20 ℃$	$M - P A A 60 ℃$	$M - P A A 100 ℃$	$H - P A A 140 ℃$	$M - P A A 140 ℃$
$A H B M, T$	2.02	190.10	176.40	137.80	107.40	60.87	40.89
$f H B M, T$	0.0100	0.9410	0.8736	0.6822	0.5317	0.3013	0.2024
$f f M, T$	0.9900	0.0590	0.1264	0.3178	0.4683	0.6987	0.7976
$γ (M, T) s, p$	34.00	7.72	12.70	14.70	18.80	23.00	25.60

Table 2 Summary of the values of AHBM,T,fHBM,T,ffM,T and γM,Ts,p of as-prepared COOH⁃SAMs and PAA thin films

COOH Surface	COOH⁃SAMs	$H - P A A 20 ℃$	$M - P A A 20 ℃$	$M - P A A 60 ℃$	$M - P A A 100 ℃$	$H - P A A 140 ℃$	$M - P A A 140 ℃$
$A H B M, T$	2.02	190.10	176.40	137.80	107.40	60.87	40.89
$f H B M, T$	0.0100	0.9410	0.8736	0.6822	0.5317	0.3013	0.2024
$f f M, T$	0.9900	0.0590	0.1264	0.3178	0.4683	0.6987	0.7976
$γ (M, T) s, p$	34.00	7.72	12.70	14.70	18.80	23.00	25.60

Fig.4 Summary of the literature⁃reported water contact angles(θ) and corresponding polar components of surface free energy(γs,p) for COOH⁃SAMs surfaces at different ∑COOH values, together with theoretical γs,p values calculated without hydration(γHBs,p and γfs,p) and with hydration (γf, hydras,p), as well as the corresponding theoretical contact angles θHBcal, θfcal and θf,hydracal(A), schematic illustration of the monolayer structure of COOH groups organized in a hexagonal arrangement(B), histogram of ff,hydra andfHB⁃Cplx values for COOH⁃SAMs surfaces at different ∑C OOH values(C) and summary of l, s, s/d2 and N¯H2O for COOH⁃SAMs surfaces at different ∑COOH values(D)

References 35

[1]	Lee H.， Alcaraz M. L.， Rubner M. F.， Cohen R. E.， ACS Nano， 2013， 7（3）， 2172—2185
[2]	Arima Y.， Iwata H.， Biomaterials， 2007， 28（20）， 3074—3082
[3]	Cheng Y.， Feng F.， Zhu T. X.， Zheng Y. H.， Gou Y. K.， Yang D. P.， Huang J. Y.， Lai Y. K.， Jiang Z. Y.， Chem. Eng. J.， 2025， 504， 158421
[4]	Rac V.， Lević S.， Balanč B.， Graells B. O.， Bijelić G.， Colloid. Surface. B， 2019， 180， 441—448
[5]	Xu Z.， Song K.， Yuan S. L.， Liu C. B.， Langmuir， 2011， 27（14）， 8611—8620
[6]	Major R. C.， Houston J. E.， McGrath M. J.， Siepmann J. I.， Zhu X. Y.， Phys. Rev. Lett.， 2006， 96， 177803
[7]	Tu A.， Kwag H. R.， Barnette A. L.， Kim S. H.， Langmuir， 2012， 28（43）， 15263—15269
[8]	Arima Y.， Iwata H.， J. Mater. Chem.， 2007， 17， 4079—4087
[9]	Choi S.， Yang Y.， Chae J.， Biosens. Bioelectron.， 2008， 24（4）， 893—899
[10]	Ohnuki H.， Izumi M.， Lenfant S.， Guerin D.， Imakubo T.， Vuillaume D.， Appl. Surf. Sci.， 2005， 246（4）， 392—396
[11]	James M.， Darwish T. A.， Ciampi S.， Sylvester S. O.， Zhang Z. M.， Ng A.， Gooding J. J.， Hanley T. L.， Soft Matter， 2011， 7， 5039
[12]	Winter N.， Vieceli J.， Benjamin I.， J. Phys. Chem. B， 2008， 112（2）， 227—231
[13]	Xu Z.， Song K.， Yuan S. L.， Liu C. B.， Langmuir， 2011， 27（14）， 8611—8620
[14]	Szori M.， Jedlovszky P.， Roeselova M.， Phys. Chem. Chem. Phys.， 2010， 12， 4604—4616
[15]	Osnis A.， Sukenik C. N.， Major D. T.， J. Phys. Chem. C， 2012， 116（14）， 770—782
[16]	Stevens M. J.， Grest G. S.， Biointerphases， 2008， 3， FC13—FC22
[17]	Ma Z. Y.， Wang D. Y.， Colloid. Surface. A， 2023， 675， 132031
[18]	Guo P.， Tu Y. S.， Yang J. R.， Wang C. L.， Sheng N.， Fang H. P.， Phys. Rev. Lett.， 2015， 115， 186101
[19]	Fowkes M.， J. Ind. Eng. Chem.， 1960， 12， 40—52
[20]	Yamakawa H.， Modern Theory of Polymer Solutions， Harper & Row， New York， 1971
[21]	Cranford S. W.， Buehler M. J.， Macromolecules， 2012， 45（19）， 8067—8082
[22]	Han T. Y.， Ma Z. Y.， Wang D. Y.， ACS Macro Lett.， 2021， 10， 354—358
[23]	Kurapati R.， Natarajan U.， Ind. Eng. Chem. Res.， 2020， 59， 16099—16111
[24]	Zhang W.， Zhang Z. N.， Wang X. P.， J. Colloid Interface Sci.， 2009， 333， 346—353
[25]	Maura J. J.， Eustance D. J.， Ratcliffe C. T.， Macromolecules， 1987， 20， 196—202
[26]	Bardet L.， Cassanas⁃Fabre G.， Alain M.， J. Mol. Struct.， 1975， 24（1）， 153—164
[27]	Leyte J. C.， Zuiderweg L. H.， Vledder H. J.， Spectrochim. Acta， 1967， 23（5）， 1397—1407
[28]	Lin⁃Vien D.， Colthup N. B.， Fately W. G.， Grasselli J. G.， The Handbook of Infrared and Raman Characteristic Frequencies of Organic Molecules， Academic Press， San Diego， 1991
[29]	Chen H. C.， Lin H. C.， Chen H. H.， Mai F. D.， Liu Y. C.， Lin C. M.， Chang C. C.， Tsai H. Y.， Yang C. P.， Sci. Rep.， 2014， 4， 4425
[30]	Kim T. H.， Ahn J. H.， Choi H. K.， Choi Y. J.， Cho C. S.， Arch. Pharm. Res.， 2007， 30， 381—386
[31]	Hoerter M.， Oprea A.， Barsan N.， Weimar U.， Sens. Actuat. B， 2008， 134（2）， 743—749
[32]	Itoh K.， Yaita M.， Hasegawa T.， Fujii S.， Misono Y.， J. Electron Spectrosc. Relat. Phenom.， 1990， 54/55， 923—932
[33]	Benoit R. L.， Louis C.， Fre’chette M.， Thermochimica Acta， 1991， 176， 221—232
[34]	Du D. M.， Qin M.， Zhou Z. Y.， Fu A. P.， Int. J. Quantum Chemistry， 2012， 112（2）， 351—358
[35]	Marcus Y.， Chem. Rev.， 1988， 88， 1475—1498