Acrylamide (AAm), the initiator-ammonium persulfate (APS), the activator N,N,N’,N’-tetramethylethylenediamine (TEMED) and zeolite (ZEO) were supplied by Sigma, Steinheim, Germany. Anionic co-monomer such as sodium vinylsulfonate (vinylsulfonic acid, sodium salt-tech. 25 wt% solution in water) (SVS) and a multifunctional crosslinker such as poly (ethylene glycol) diacrylate (PEGDA, M_n = 700) as a crosslinker were supplied from Aldrich, Steinheim, Germany. Sodium carboxymethyl cellulose (CMC) was purchased from Fluka, Steinheim, Germany [20]. The solvents that were used in swelling studies, acetone (ACE), methanol (MET) and tetrahydrofuran (THF) were supplied by Riedel de Haën, Germany. All chemicals were used as received.

The hydrogels, the semi-interpenetrating polymer networks, and the hybrid/biohybrid composite hydrogel systems developed in this study were prepared by free radical crosslinking copolymerization of AAm monomer with addition of SVS and a multifunctional crosslinker such as PEGDA as a crosslinker [20]. Highly swollen AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels were prepared by free radical crosslinking copolymerization of AAm monomer with addition of an anionic comonomer such as SVS and a multifunctional crosslinker such as PEGDA. The modes of purification and specifications of the sources of water, the monomers AAm and SVS, crosslinker; PEGDA, initiator; APS and activator; TEMED were given in our related study [20].

In our previous study, water sorption and dye uptake properties of highly swollen AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels have been reported [20]. But, it would be better than, if some details of the synthesis of the hydrogel systems can be given, again. To prepare highly swollen and chemically crosslinked AAm hydrogel systems, AAm weighing 1.0 g/14.07 mmol was dissolved in 1.0 mL water. Then, 60 μL (0.544 mmol) of SVS was added to aqueous other AAm solution (for AAm/SVS hydrogels containing 60 μL of SVS) at room temperature, (25˚C). Then, 120 μL (1.088 mmol), 180 μL (1.633 mmol), 240 μL (2.176 mmol), and 300 μL (2.72 mmol) of SVS were added to other aqueous AAm solutions, respectively for containing different amount of SVS in AAm/SVS hydrogel systems. After these additions, for the synthesis, 0.25 mL/0.004 mmol of 1% concentration of PEGDA and 0.2 mL/0.044 mmol aqueous solutions of APS ( 5.0 g APS/100 mL water) and 0.25 mL/0.017 mmol 1% concentration of TEMED were added these aqueous solutions (Table 1) [20].

In preparation, the solutions were placed in special cylindrical plastic molds (having 7.0 mm of diameter and 3.0 mm of height) (Figure 1), then, they waited for an hour for gelation. After gelation, the samples were washed with distilled water by several times. Then, they were dried in air and vacuum, and stored for swelling studies [20].

For the synthesis of AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid

hydrogels and AAm/SVS/CMC/ZEO biohybrid hydrogels, the modes of specifications of the sources of water, the monomers AAm and SVS, ZEO, polysaccharide; CMC, crosslinker; PEGDA, initiator; APS and activator; TEMED were given in our related study [20]. For synthesis of all used samples in this study, the quantities of AAm, SVS, CMC and ZEO were presented in Table 1. Schematic representation of preparation of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels have been presented in Figure 1.

The dried hydrogels were immersed in water, in pure solvents such as ACE, MET and THF, and water-solvent (ACE, MET and THF) binary mixtures of various compositions. The gravimetric method was employed to study the swelling characterization. Swollen gels were removed from water, pure solvents and binary mixtures of water-60% of solvent (ACE, MET and THF) at predetermined times, blotted dry, and weighed in air. Water, pure solvents and water-solvent binary mixtures were kept at 25˚C ± 0.1˚C to allow the hydrogels to reach equilibrium for examines of solvent composition effect on swelling properties of the hydrogel systems [5].

In the next swelling tests, for the investigation of the effect of composition of solvent on swelling, highly swollen AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels containing 240 μL SVS have been swollen at water and binary mixtures of various compositions such as water-20%; 40%; 60% and 80% of solvent (ACE, MET and THF). From these measurements, some swelling and diffusion parameters have been determined [5].

The water, some solvents such as ACE, MET and THF, or some liquids such as water/solvent binary mixtures intake of initially dry hydrogels was followed for novel AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels. The hydrogels were waited in water, in solvents and in binary mixtures of various compositions of water-solvent (ACE, MET and THF). Here it was seen that there is no swelling in 100% composition of the solvents such as ACE, MET and THF [5].

The water or binary mixtures of various compositions of water-solvent (ACE, MET and THF) intake of initially the hydrogels were followed for a period of time, gravimetrically. The swelling factor (S) of the hydrogels in distilled binary mixtures of various compositions of water-solvent (ACE, MET and THF) was calculated from the following relation [5] [20].

S = m t − m o m o (1)

Here, m_t is the mass of the swollen gel at time t and m_o is the mass of the dry gel at time 0. The liquid intake of initially dry hydrogels was followed for novel AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels crosslinked by PEGDA in water or binary mixtures of various compositions of water-solvent (ACE, MET and THF), and swelling isotherms of AAm/SVS hydrogels in water-60% of MET have shown in Figure 5 as representative. As shown in Figure 5, AAm/SVS hydrogels have the lower swelling factor (S) values in water-60% of MET.

Figure 5 shows that swelling, or sorption of liquid (water/or binary mixtures of the solvents) increases with time up to certain level, and then levels off. This value of swelling factor (S) may be called as the “equilibrium swelling factor” (S_eq). S_eq values of the hydrogel systems are given in Table 2. Table 2 shows that S_eq of AAm hydrogels is 7.724, but S_eq of AAm/SVS hydrogels are 9.082 - 26.069 with the incorporation of SVS groups into chemically crosslinked AAm copolymers, if AAm/SVS hydrogels have been swollen in binary mixture of water-60% of ACE. The other S_eq values of the hydrogels have been presented in Table 2 for binary mixture of water-60% of MET and binary mixture of water-60% of THF, too.

In Table 2, S_eq of the hydrogels increased with SVS content in the hydrogel systems. Hydrophilicity of SVS molecules becomes greater than that of AAm, so,

the swelling of AAm/SVS is greater than the swelling of AAm hydrogels. AAm/SVS hydrogels strong electrostatic interactions are present due to strongly dissociated charged groups of SVS units [20]. SVS contains many ionic units (Figure 2). The swelling increase is due to an increase in the anionic units. Here, the main effect is the hydrophilic character of SVS. It is well known that the swelling of a hydrogel is induced by the electrostatic repulsion of the ionic charges of its network. The ionic charge content is important. The salt group is almost completely ionized, and a large number of hydrophilic group occur [20].

S_eq of AAm/SVS/ZEO hybrid hydrogels containing 1.0% of ZEO is 7.980 - 24.989 with the incorporation of ZEO groups into AAm/SVS hydrogels, while S_eq of AAm/ZEO hybrid hydrogels is 6.614. On the other hand, the values of S_eq of AAm/SVS/CMC semi IPNs containing 1.0% of CMC are 10.278 - 31.977 with the incorporation of CMC into AAm/SVS hydrogels, while S_eq of AAm/CMC semi IPNs is 7.629 in water [20]. When solvent and water are mixed, it was seen that important decreasing at swelling values. Table 2 shows that the value of S_eq of the hydrogels is 0.733 - 0.989 for water-60% of ACE, 0.872 - 1.509 for water-60% of MET, and 1.288 - 2.215 for water-60% of THF.

The values of S_eq of AAm/SVS/CMC/ZEO biohybrid hydrogels containing 1.0% of CMC and 1.0% of ZEO are 10.168-26.026 with the incorporation of CMC and ZEO into AAm/SVS hydrogels, while S_eq of AAm/ZEO/CMC biohybrid hydrogels is 6.715 (Table 2). In Table 2, the values of S_eq of the hydrogels increased with the SVS content in the crosslinked copolymers. S_eq of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels are higher than S_eq of AAm hydrogels. Also, this hydrophilic effect has been shown in our previous studies using some hydrophilic co-monomers such as sodium acrylate [21], 2-acrylamido- 2-methyl-1-propanesulfonic acid [22], 4-styrenesulfonic acid sodium salt [23], and maleic acid [24]. In these studies, the swelling or water sorption increase is due to an increase in the anionic units [5] [20] [21] [22] [23] [24]. It is well known that the swelling of a hydrogel is induced by electrostatic repulsion of the ionic charges of its network. The salt group is almost completely ionized, and a large number of hydrophilic groups occur. An anionic co-monomer such as SVS contains ionizable groups, so more SVS groups on the copolymeric chain contain many ionizable groups. The hydrophilic group numbers of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels are higher than those of AAm, and so, the values of S_eq of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/ SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels were greater than that of the values of S_eq of AAm [5] [20] [21] [22] [23] [24].

It was shown that a partially decrease of the values of S_eq of AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels when CMC and ZEO have been added to the hydrogel systems. Incorporation of CMC and ZEO into the copolymer network leads to lower degrees of swelling in water [20]. The reason of this may be the polymeric structure of CMC and structure of ZEO. Here, it could be said that a lot of number of group of CMC and/or ZEO chains were placed in the crosslinked polymeric systems, instead of crosslinked AAm and SVS monomers. So, it was seen that decreasing of the value of S_eq, because of decreasing of partially hydrophilic character at crosslinked polymeric systems. But, on the other hand, it can be said that there is no good relationship between the values of S_eq of the hydrogels, when CMC and/or ZEO have been added to the polymeric systems [20]. The same characteristic swelling behavior and results could have been followed, if there have been investigated that the results of swelling studies of the hydrogels in binary mixtures of various compositions of water-solvent (ACE, MET and THF). Again here, it can be said that there was no good relationship between the values of S_eq of the hydrogels, when CMC and/or ZEO have been added to the polymeric systems.

For understanding the effect of SVS content on the swelling behavior in water, in water-60% of ACE, in water-60% of MET and in water-60% of THF, the values of S_eq of the hydrogels versus the content of SVS is plotted in Figures 6-9. In Figures 6-9, the values of S_eq of the hydrogels gradually increased with increasing of SVS content in the hydrogels.

The water or liquid absorbed by AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels and AAm/SVS/CMC/ZEO biohybrid hydrogels quantitatively represented by equilibrium water/liquid capacity (EWLC) also, and they can be calculated by below equation [25] [26] [27].

EWLC = m e q − m o m e q (2)

Here, m_eq is the mass of the swollen gel at time t (equilibrium), and m_o is the mass of the dry gel at time 0. The values of EWLC of the hydrogel systems were

calculated. These values of EWLC of the hydrogels are tabulated in Table 3. They are changed between 0.4118 - 0.9697. It is seen that an increasing of the values of EWLC, if SVS has been added to the hydrogel systems. Here, the main effect is the hydrophilic character of SVS groups. But, it has been seen that increasing of the values of EWLC, if CMC and/or ZEO have been added to the hydrogel systems if there have been investigated that the values of EWLC of the hydrogels in binary mixtures of various compositions of water-solvent (ACE, MET and THF). Again here, it can be said that there was no good relationship between the values of EWLC of the hydrogels, when CMC and/or ZEO have been added to the polymeric systems.

Here, the main effect is the hydrophilic character of SVS monomer and non-hydrophilic character of the solvents as mentioned before then.

Diffusion involves migration of water or water-solvent binary mixtures into pre-existing or dynamically formed spaces between hydrogel chains. Swelling of

the hydrogel involves larger segmental motion resulting, ultimately, in increased separation between hydrogel chains. When a glassy hydrogel is brought into contact with water or water-solvent mixtures, water or water-solvent mixtures diffuses into the hydrogel and the network expands resulting in swelling of the hydrogel.

Analysis of the mechanisms of water or water-solvent binary mixtures diffusion into swellable polymeric systems has received considerable attention in recent years, because of important applications of swellable polymers in biomedical, pharmaceutical, environmental, and agricultural processing. The following equation is used to determine the nature of diffusion of water or water-solvent mixtures into hydrogels [27] [28] [29].

F = M t M s = k t n (3)

Here, F is the fractional uptake at time t; M_t and M_s are the mass uptake of the water or water-solvent mixtures at time t and the equilibrium, respectively. Equation (3) is valid for the first 60% of the fractional uptake. Fickian diffusion and Case II transport are defined by n values of 0.5 and 1.0, respectively. Anomalous transport behavior (non-Fickian diffusion) is intermediate between Fickian and Case II. That is reflected by n between (0.5) and (1.0) [28] [29]. The values of n and k were calculated from the slope and the intercept of the plot of lnF against lnt, respectively.

For chemically crosslinked highly swollen AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels, the plots of lnF vs. lnt where F is equal to (M_t/M_s) are shown in Figure 10 for AAm/SVS/ZEO hybrid hydrogels in water-60% of ACE, as representative. Diffusional exponents (n) and diffusion constant (k) are calculated from the slopes and intercepts of the lines, respectively, and are listed in Tables 4-6.

Tables 4-6 show that the values of the number determining the type of diffusion (n) are between 0.5003 - 0.6758. Hence the diffusion of binary mixtures of water-solvent (60% of solvent (ACE, MET and THF) of various compositions into the hydrogel systems is generally found to have a non-Fickian character. When the diffusion type is anomalous behavior, the relaxation and diffusion time are of the same order of magnitude [28] [29]. Tables 4-6 show that the number determining the type of diffusion, n is over 0.50. Hence the diffusion of water or water-solvent mixtures into the hydrogels is generally found to have a non-Fickian character [28] [29]. When the diffusion type is anomalous behavior, the relaxation and diffusion time are of the same order of magnitude [28] [29].

The study of diffusion phenomena of water or water-solvent binary mixtures in hydrogels is of value in that it clarifies polymer behavior. For hydrogel characterization, the diffusion coefficients can be calculated by various methods. The diffusion coefficient, D of the water or water-solvent mixtures was calculated using the following equation [30] [31].

D = π r 2 ( k 4 ) 1 / n (4)

Here D is in cm²∙s⁻¹, r is the radius of a cylindrical polymer sample, n is the diffusional exponent and k is a constant incorporating characteristic of the macromolecular network system and the penetrant. The values of diffusion coefficient determined for the hydrogels are listed in Tables 4-6. Tables 4-6 show that the values of the diffusion coefficient of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels vary from 1.59 × 10⁻⁴ cm²∙s⁻¹ to 8.34 × 10⁻⁴ cm²∙s⁻¹ for water [20], but the values of the diffusion coefficient of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels vary from 3.962 × 10⁻⁵ cm²∙s⁻¹ to 20.131 × 10⁻⁵ cm²∙s⁻¹ for binary mixtures of water-solvent (60% of ACE, 60% of MET and 60% of THF). It can be said that there is no good relationship between the values of the diffusion coefficient of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels for binary mixtures of water-solvent (60% of ACE, 60% of MET and 60% of THF).

Other important diffusion parameters can be “water/liquid sorption rate constant” (K_sr). This parameter can be calculated by the presented at below equation [5] [20] [32].

− ln ( 1 − F ) = K s r t + E (5)

where t is sorption time, “K_sr” is water/liquid sorption rate constant. F was described before, and E is a constant. For chemically crosslinked highly swollen AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels, the plots of [–ln(1 − F)] vs [t] where F is equal to (M_t/M_s) are shown in Figure 11 for AAm/SVS/ZEO hybrid hydrogels in water-60% of ACE, as representative.

The water sorption rate constants of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid

hydrogels calculated from the slope of the plots, and they are tabulated at Tables 4-6. They are changed among range vary from 1.424 × 10⁻³ min⁻¹ to 13.7890 × 10⁻³ min⁻¹. Tables 4-6 showed that water/liquid sorption rate constants of AAm/ SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels are generally lower than that of AAm hydrogels, AAm/CMC semi IPNs, AAm/ZEO hybrid hydrogels, and AAm/CMC/ZEO biohybrid hydrogels. The reason of this may be the hydrophilic and ionic characteristics of SVS. Every SVS molecule has got an anionic group such as vinylsulfonate group having negative charge. Because of the more charged structure, water sorption into the hydrogel systems may be irregular. On the other hand, it can be said that more irregular forms could be occurred in cross-linked structure by adding of CMC and/or ZEO.

For investigation of the effect of mass/content of CMC and ZEO on the swelling and diffusional properties of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels, the related swelling isotherms and related swelling kinetic curves of hydrogel systems were constructed and, plots of lnF versus lnt for AAm/SVS/CMC semi IPN hydrogels containing 240 μL of SVS and different contents of CMC was shown in Figure 12 as representative. Effect of CMC and ZEO on some swelling, kinetics and diffusion parameters of AAm/SVS/CMC semi IPNs and AAm/SVS/ZEO hybrid hydrogels having of 240 μL SVS with different volume (as mL) of 2.0% of ZEO-water suspension or 2.0% of aqueous CMC solutions were tabulated in Table 7 and Table 8.

It was shown that an increasing of the values of S_eq of AAm/SVS/CMC semi

IPNs and AAm/SVS/ZEO hybrid hydrogels having of 240 μL SVS with different CMC and different ZEO contents, when CMC and ZEO have been added to the hydrogel systems. Incorporation of CMC and ZEO into the copolymer network leads to higher values of S_eq. The reason of this increase may be the polymeric structure and partially hydrophilic character of CMC and ZEO. So, it was seen that increasing of the value of the S_eq, because of increasing of hydrophilic character at cross-linked polymeric systems. On the other hand, again it can be seen that similar characteristic behavior on the some swelling, kinetics and diffusion parameters, if Tables 4-6 have been investigated.

Swelling of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogel may be evaluated by the composition of solvent. Variations of the swelling factor (S) of the hydrogels as a function of the solvent contents/concentration in the binary mixtures of water-solvent have been plotted in Figures 13-16. The values of some swelling and diffusion parameters of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogel systems in water or binary mixture of water-solvent (ACE, MET and THF) were tabulated in Tables 9-12.

In Tables 9-12, the values of S_eq of the hydrogels in binary mixture of water-solvent (ACE, MET and THF) are lower than the value of the hydrogels swollen in water. MET has got one alkyl group, but ACE and THF have got more than alkyl group from MET. With the increasing of alkyl group in the solvent, water diffusion can be affected by the depending on organic molecular structure and pores of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels.

It was seen that decreasing of the value of S_eq of the hydrogels with the increasing composition of the solvents. Here, an important reason, the hydrophobic character of the alkyl groups in the molecular structure. The hydrophobic character can be increased with the increasing of alkyl group of the organic molecular structure. For this reason, the more hydrophobic groups in the solvents get the less the swelling of the hydrogels in binary mixtures of water-solvent (in ACE, in MET and in THF). Again Tables 9-12 show that the values of S_eq for binary mixtures of water-20%; 40%; 60%; and 80% of ACE are 0.372 - 21.038, for binary mixtures of water-20%; 40%; 60%; and 80% of MET are 0.499 - 21.289, and for binary mixtures of water-20%; 40%; 60%; and 80% of THF are 0.744 - 18.784.

For the swelling of AAm/SVS hydrogels, AAm/SVS/CMC semi IPNs, AAm/ SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ZEO biohybrid hydrogels in binary mixtures of water-solvent (in ACE, in MET and in THF), it can be expected different behavior in water. This difference can be explained by the dependence of the ionization of the charged groups of the hydrogels in various compositions of binary mixtures of water-solvent. Because of the lower polarisability, high hydrophobicity, and the lower hydrogen bonding occurring in swelling, the swelling value of the hydrogels can be lower than the swelling in water. Also for good description of content of SVS on swelling characterization, column plots of S_eq versus various contents of SVS for AAm/SVS hydrogels, AAm/ SVS/CMC semi IPNs, AAm/SVS/ZEO hybrid hydrogels, and AAm/SVS/CMC/ ZEO biohybrid hydrogels including of various contents of SVS could have been discussed here again (Figures 6-9). It was seen that the values of S_eq of the hydrogels increased with the SVS content in the crosslinked copolymers, again.