# Alkylimidazolic Ionic Liquids Absorption and Diffusion in Wood
## 3 Results and Discussion  
For all the wood samples, the absorbed amount of ionic liquids is 30 to 85% higher than that corresponding to distilled water, demonstrating the wood matrix's high affinity for these compounds [14,15]. As an absorption trend, the uptake of ILs is strongly dependent on the molecular mass of the cation, i.e., EMIM\({}^{+}\) > BMIM\({}^{+}\) > HMIM\({}^{+}\) (Figure 1a-c). Chlorides are absorbed in a higher amount than acetates and tetrafluoroborates due to their higher interaction potential with the cellulose and lignin components of the wood, as found in the reference literature [29,30]. Figure 1: (**a**) Relative amount of ILs absorbed at equilibrium in spruce and beech wood; (**b**) specific mass of absorbed ILs at equilibrium for spruce and beech wood; (**c**); wood percent gain of spruce and beech wood swollen in ILs; (**d**) relative volumetric modifications of spruce and beech wood swollen in ILs; (**e**) kinematic viscosities of the ILs at 25 \({}^{\circ}\)C; and (**f**) surface tension of the ILs at 25 \({}^{\circ}\)C.  
The uptake and swelling are marginally higher for spruce due to its looser microstructural packing than been [31; 32]. IL penetration into the wood determines much higher relative volume modifications (\(\Delta\)V, %, Figure 1d) than in the case of water, which makes ILs useful as the transport media of various preservatives and impregnates (oligomeric resins, monomers) into the bulk of the wood. The permeability of ILs into the wood structure is also influenced by their relative viscosity. For the same anion type, viscosity is dependent on the molar mass of the cation (Figure 1e), as lateral alkyl chains of higher dimensions promote van der Waals interactions which impede the sliding of the molecules past each other. All of the studied ionic liquids are tensioactive, which improves the wetting of the wood capillaries and aids adsorption and diffusion (Figure 1f). An Anderson-Darling statistical analysis is performed to determine if the dependencies of the amount of ILs absorbed at the equilibrium (\(w_{IL,eq}\)), relative to the volume modification (\(\Delta\)V, %) and surface tension (\(\gamma\))/viscosity of the ILs (\(\eta\)), are normally distributed (Minitab 19 software). A correlation test is performed to test if there is a strong correlation between the variables at a 95% confidence level. The results are depicted in Table 1. From the available data, only the values of viscosity and surface tension for the ILs with EMIM, BMIM, HMIM cations, and Cl\({}^{-}\), BF\({}_{4}\)\({}^{-}\) anions are selected (not all the cations are paired with acetate anions). As shown in Table 1, since the value of the \(p\) coefficient for normality testing is in all instances higher than 0.05, it can be assumed that the studied data are part of a normal distribution. With this assumption, the statistical correlation analysis indicates a strong positive correlation between the surface tension of the ILs (which is dependent on its structure) and their uptake for both types of wood. The higher the uptake of ILs, the higher the relative modifications in volume for the samples. Uptake and relative volume modifications seem to be moderately dependent on the viscosity of the ILs. The higher the viscosity, the lower the absorbed amount (hence the negative value for \(r\)). The correlations between the viscosity of ILs and their uptake in wood seem to be less positively correlated for beech, most likely due to its more complex anatomy. A higher ionic liquid viscosity can also mean that the IL is predominantly distributed near the surface of the wood, being less effective in promoting bulk volume modifications in general. For all the studied ILs and wood types, ILs penetration into the bulk of the wood and reaching of the sorption equilibrium occurs much faster than in the case of moisture, e.g., for all the ILs, the