Predictive modelling of the water contact angle of surfaces using attenuated total reflection – Fourier transform infrared (ATR-FTIR) chemical imaging and partial least squares regression (PLSR)

Abstract

The static water contact angle (CA) quantifies the degree of wetting that occurs when a surface encounters a liquid, e.g. water. This property is a result of factors such as surface chemistry and local roughness and is an important analytical parameter linked to the suitability of a surface for a given bioanalytical process. Monitoring the spatial variation in wettability over surfaces is increasingly critical to analysts and manufacturers for improved quality control. However, CA acquisition is often time-consuming because it involves measurements over multiple spatial locations, independent sampling and the need for a single instrument operator. Furthermore, surfaces exposed to local environments specific to an intended application may affect the surface chemistry thereby modifying the surface properties. In this study, Attenuated Total Reflection-Fourier Transform Infrared (ATR-FTIR) chemical imaging data acquired from wet and dry polymer surfaces were used to develop multivariate predictive models for CA prediction. Partial Least Squares Regression (PLSR) models were built using IR spectra from surfaces presenting differences in the experimentally measured CA in the range 16°-141°. The best performing PLSR models were locally developed and combined to make a global model utilising wet IR spectra which performed well (R2p = 0.98, RMSECV ∼ 5°) when tested on an independent experimental set. This model was subsequently applied to IR spectra acquired from a surface exhibiting spatial differences in surface chemistry and the CA with a reasonable confidence and precision (prediction error within 10°), demonstrating the potential of this method for prediction of the spatially varying CA as a non-destructive in-line process monitoring technique.

Surface Etching of 3D Printed Poly(lactic acid) with NaOH: A Systematic Approach

“…However, these models are for idealized surfaces and have their limitations in the description of real surfaces [35]. Mukherjee et al [36] described a model of the contact angle of different surfaces and the influence of roughness and chemical properties. Their data are consistent to our observations that roughness increases the CA and a more surface with stronger chemical interactions between surface and water leads to lower CA.…”

Predictive Modeling of the In Vitro Responses of Preosteoblastic MC3T3-E1 Cells on Polymeric Surfaces Using Fourier Transform Infrared Spectroscopy

“…PVC shows the highest surface variation in CA with standard deviation of 7°, which corresponds to the spatial heterogeneity detected by spectral variation in Figure S3. Mukherjee et al 8 also stated the same finding that PVC demonstrated the highest standard deviation of CA values among all the chosen polymers. 1, where live cells are labeled in green and dead cells in red.…”

“…Using the technique developed by Mukherjee et al, wetted spectra were acquired after hydrating the sample at room temperature (21–25 °C and 40–60% relative humidity) with an equilibration time of ∼30 min. A Press-to-Seal (Sigma-Aldrich Ireland, Ltd.) silicone isolator was applied on the surface of sample materials using gentle pressure to construct a sealed isolated region where water can be trapped to generate wet surfaces.…”

“…ATR-FTIR has been reported to investigate protein adsorption on biomaterials, surface segregation, and restructuring in poly­( l -lactide) and poly­( d , l -lactide- co -glycolide) films and degradation in polycarbonate urethane (PCU) biomaterials . Recently, Mukherjee et al applied ATR–FTIR chemical imaging to develop multivariate models for prediction of surface wettability of polymeric materials. Good results were obtained with R 2 P of 0.98 and root-mean-square errors of prediction (RMSEP) around 5° when tested on an independent experimental set.…”

Durable and Superhydrophobic Aluminium Alloy with Microscale Hierarchical Structures and Anti-Drag Function Inspired by Diving Bell Spider

“…Generally, when the contact angle of the surface is greater than 90 • , it is defined as a hydrophobic surface. In particular, when the contact angle is greater than 150 • and the sliding angle (SA) is less than 10 • , water droplets could maintain a spherical shape on the solid surface, which is called a superhydrophobic surface [9][10][11][12]. However, the conventional superhydrophobic paint focuses on enhancing the water-repellent performance solely, which neglects the physicochemical durability [6,[13][14][15].…”