Iron complexes embedding influence on PMAA hydrogel

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Iron complexes embedding influence on PMAAhydrogelTo cite this article L Khenkin et al 2012 IOP Conf Ser Mater Sci Eng 38 012029

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Iron complexes embedding influence on PMAA hydrogel

L Khenkin1 T Baluyan A Novakova I Rebrin E Makhaeva

MVLomonosov MSU physics department Moscow Russia

E-mail levkhenkingmailcom

Abstract The interaction of weakly cross-linked gel of poly(methacrylic acid) with iron

complexes results in Fe2+

absorption additional cross-links and therefore gel collapses Lattice

dynamics of frozen investigated samples were examined by means of Mossbauer spectroscopy

in order to find out the mechanism of metal-polymer bonding It was established that iron

complexes form strong bonds with polymer functional groups contracting gel network

1 Introduction

Poly(methacrylic acid) (PMAA) groups can show specific interactions such as hydrogen bonding

acidndashbase interactions and ionic interactions of opposite charges which can help to prepare novel self-

organized materials Numerous studies have been also devoted to the interaction of PMAA with metal

ions since knowledge of association phenomena of metal ions with charged macromolecules is of

importance for the understanding of their physicochemical behavior in environmental and biological

systems PMAA could be successfully used as a component of characteristic lsquointelligentrsquo organicndash

inorganic hybrid materials

The interaction of weakly cross-linked PMAA gel with iron complexes results in their absorption

and gel collapse [1 2] This collapse occurs due to iron ionspolymer functional groups bonds that

form additional cross-links contracting gel network The aim of the present work is study of molecular

lattice dynamics and metal-polymer bonds strength in PMAA geliron complexes systems by means of

Mossbauer spectroscopy

2 Experimental section

PMAA gels were prepared through radical polymerization in solution with NN-methyl-bis-

acrylamide as a cross-linker The procedure of PMAA gels treatment was the same as that described

previously [3] The degree of the polymer gel swelling (Φ) in complex solutions is defined by the ratio

of the mass of polymer gel after immersion in iron complex solution to the initial gel mass

In the present study PMAA gel was incubated in two different media aqueous solution of iron(II)

chloride and aqueous solution of ferroin (Fe2+

ndashphenanthroline complex)

Temperature-dependence of their Mossbauer spectra can serve to elucidate the bonding and

dynamical behavior of the iron ions in such systems [4] Mossbauer lattice temperatures θM and

effective vibrating mass Meff were estimated from temperature dependences of recoilless fraction and

second order Doppler shift δSOD Mossbauer spectroscopy data for all incubated PMAA gels and for

1 To whom any correspondence should be addressed

International Conference on Functional Materials and Nanotechnologies (FMampNT2012) IOP PublishingIOP Conf Series Materials Science and Engineering 38 (2012) 012029 doi1010881757-899X381012029

Published under licence by IOP Publishing Ltd 1

used frozen solutions were obtained in the temperature interval from 118K up to the Mossbauer effect

disappearance temperature

Mossbauer spectra were obtained in a standard transmission geometry using a 57

Co(Rh) gamma

source The gamma radiation was detected with a NaI(Tl) scintillation detector The spectrometer was

calibrated by a standard α-Fe absorber The spectra were analyzed using the UNIVEM MS program

(2006) which ensures fitting by a combination of Lorentzians with adjustable Mossbauer parameters

isomer shift (δ) quadrupole splitting (Δ) peak width and peak area under the curve (A)

3 Results and discussion

The swelling behavior of PMAA hydrogels was studied in [2] The degree of contraction depends on

the amount of monomers in the parent PMAA gel and the amount of absorbed Fe ions The samples

under investigation after week incubation in iron complex solution were collapsed Degree of their

swelling was Φ=022 for incubation in ferroin aqueous solution and Φ=012 for incubation in iron

chloride aqueous solution

Mossbauer spectra at T=118K and images of investigated samples are shown in figure 1 In iron

salt solution all Fe2+

ions form [Fe(H2O)6]2+

coordination entities of octahedral geometry So the

spectra of all samples comprise one component doublet with big quadrupole splitting for high-spin

Fe(II) ions in chloride salt solution and doublet with small quadrupole splitting for low-spin Fe(II)

ions in ferroin solution (see table 1 for values)

Mossbauer spectral parameters (isomer shift and quadrupole splitting) for both iron complexes

appeared to be the same in investigated aqueous solutions and in gel incubated in these solutions The

invariance of the spectral parameters reflects the iron ions environments uniformity Both ferroin and

aqua-complex remain holistic and stable after embedding to gel matrix

Figure 1 Mossbauer spectra at T=118K and photo of a) FeCl2 aqueous solution b) PMAA gel in

FeCl2 aqueous solution c) ferroin aqueous solution d) PMAA gel in ferroin aqueous solution


2

Temperature dependences of all the samples under investigation spectrum intensity (area under

curve) characterizing recoilless fraction are shown in figure 2 All dependence curves have contrary

flexure point at temperatures near 190K This feature is induced by diffusion motion of iron

complexes that will be discussed later

For molecular crystals the normal modes of vibration are usually separated into two groups the

weaker intermolecular modes related to vibrations of the molecular center of mass and the stronger

intramolecular modes of much higher frequencies within the molecule

If the molecule is an ideal rigid body the mass value in the expressions for f and δ SOD would just

be the molecular weight In reality the molecule is not entirely rigid due to some degree of internal

vibration the mass value may be replaced by an effective vibrating mass Meff Its upper limit is the

molecular weight and lower limit is the mass of the Mossbauer iron isotope (57 Da) the latter

corresponds to the situation of Fe atoms as monatomic vibrating entities in a solid

For the lower temperature area theory gives the following equations [4 5]

constTATkcM

Ef

MBeff

)(ln3

ln22

2

(1)

constcM

Tk

eff

BSOD

2

3 (2)

where A is the area under the resonance curve (ln A prop ln f = exp(-k2ltu

2gt) for an optically thin

absorber ltu2gt is the mean square amplitude of the metal atom vibration) kB - Boltzmannrsquos constant

c - velocity of light Eγ - the energy of the emitted γ-ray

Both the δ and ln A temperature dependencies for this compound are well fitted by linear

regressions (ln A for the temperature diapason from 118K to curve contrary flexure point) Curve

slopes values of the fitting lines are given in table 1 After substitution these values to (1) and (2) we

obtained effective vibrating masses and lattice temperatures for all our samples (table 1)

The deviation of the Meff values from 57 Da reflects the covalency of the bonding force between

the Fe atom and its neighbours [6] A comparison of Meff values between complexes in frozen solution

and in the PMAA gel matrix leads to conclusion that strong chemical bonds appear between the iron

complexes and the functional groups of polymer (COO-) Moreover temperature ΘM should consider

as a quantitative measure of such bonds Thus stable metal - polymer complexes formed

Figure 2 Temperature dependence A (area under curve) for a) FeCl2 aqueous solution

PMAA gel in FeCl2 b) ferroin aqueous solution PMAA gel in aqueous solution


3

Table 1 Mossbauer parameters and derived quantities of investigated samples

Measurement errors are indicated in brackets

Sample δ mms

at 118K

Δ mms

at 118K

dδ dT

10-4

mmsecK

d lnA dT

10-3

K-1

Meff Da ΘM K

FeCl2 aqueous solution 141(2) 339(3) 75 (5) 101 (5) 111 (7) 83 (7)

PMAA Gel in FeCl2

aqueous solution 138 (2) 333(3) 67 (4) 46 (3) 124 (7) 116 (9)

Feroin aqoueous solution 040 (2) 026(3) 37 (2) 81 (4) 224 (9) 65 (6)

PMAA Gel in ferroin


Temperature dependences of Mossbauer spectra line width (figure 3) give the data about increasing

of diffusion motion with increasing temperature Spectra of samples in the chloride solution had

significantly broader lines than spectra for ferroin solution because of higher molecular mobility of

aqua molecules from nearest iron surrounding On warming towards the melting point the relaxation

time for diffuse jumps of the resonance atoms becomes of the same order of magnitude as excited state

lifetime [7] So at elevated temperatures diffusive motion increases rapidly Line broadening in frozen

PMAA gel incubated in ferroin solution started at the temperature on 20K higher

4 Conclusion

All obtained data allow us to conclude that investigated iron complexes (ferroin and aquacomplex)

embed in PMAA gel network without destruction and form strong bonds with polymer functional

groups These bonds are stronger than iron complexes bonds in frozen aqueous solutions crystal And

these bonds have higher degree of covalence Such stability of iron complexes inside the polymer gel

matrix could be widely used in practical applications

References

[1] Grigorrsquoev T E Nguen K H Skryabina I V Makhaeva E E and Khokhlov A R 2008

Polym Sci A 50 68

[2] Starodoubtsev S G Khokhlov A R Sokolov E L and Chu B 1996 Macromolecules 28 3930

Figure 3 Line width temperature dependence for all investigated samples


4

[3] Khenkin L V Shishakov A I Novakova A A Kozhunova E Yu and Makhaeva E E 2011

Inorganic Materials 47 1271

[4] Chen Y L and Yang D P 2007 Mossbauer Effect in Lattice Dynamics (Weinheim Wiley-VCH)

[5] Herber R H and Nowik I 2008 J Nucl Radiochem Sci 9 33

[6] Long G J Hautot D Grandjean F Morelli D T and Meisner G P 2000 Phys Rev B 62 6829

[7] Singwi K S and Sjolander A1960 Phys Rev 120 1092


5

Iron complexes embedding influence on PMAA hydrogel

L Khenkin1 T Baluyan A Novakova I Rebrin E Makhaeva

MVLomonosov MSU physics department Moscow Russia

E-mail levkhenkingmailcom

Abstract The interaction of weakly cross-linked gel of poly(methacrylic acid) with iron

complexes results in Fe2+

absorption additional cross-links and therefore gel collapses Lattice

dynamics of frozen investigated samples were examined by means of Mossbauer spectroscopy

in order to find out the mechanism of metal-polymer bonding It was established that iron

complexes form strong bonds with polymer functional groups contracting gel network

1 Introduction

Poly(methacrylic acid) (PMAA) groups can show specific interactions such as hydrogen bonding

acidndashbase interactions and ionic interactions of opposite charges which can help to prepare novel self-

organized materials Numerous studies have been also devoted to the interaction of PMAA with metal

ions since knowledge of association phenomena of metal ions with charged macromolecules is of

importance for the understanding of their physicochemical behavior in environmental and biological

systems PMAA could be successfully used as a component of characteristic lsquointelligentrsquo organicndash

inorganic hybrid materials

The interaction of weakly cross-linked PMAA gel with iron complexes results in their absorption

and gel collapse [1 2] This collapse occurs due to iron ionspolymer functional groups bonds that

form additional cross-links contracting gel network The aim of the present work is study of molecular

lattice dynamics and metal-polymer bonds strength in PMAA geliron complexes systems by means of

Mossbauer spectroscopy

2 Experimental section

PMAA gels were prepared through radical polymerization in solution with NN-methyl-bis-

acrylamide as a cross-linker The procedure of PMAA gels treatment was the same as that described

previously [3] The degree of the polymer gel swelling (Φ) in complex solutions is defined by the ratio

of the mass of polymer gel after immersion in iron complex solution to the initial gel mass

In the present study PMAA gel was incubated in two different media aqueous solution of iron(II)

chloride and aqueous solution of ferroin (Fe2+

ndashphenanthroline complex)

Temperature-dependence of their Mossbauer spectra can serve to elucidate the bonding and

dynamical behavior of the iron ions in such systems [4] Mossbauer lattice temperatures θM and

effective vibrating mass Meff were estimated from temperature dependences of recoilless fraction and

second order Doppler shift δSOD Mossbauer spectroscopy data for all incubated PMAA gels and for

1 To whom any correspondence should be addressed


Published under licence by IOP Publishing Ltd 1




Co(Rh) gamma

























2














constTATkcM

Ef

MBeff

)(ln3

ln22

2

(1)

constcM

Tk

eff

BSOD

2

3 (2)

















3



Sample δ mms

at 118K

Δ mms

at 118K

dδ dT

10-4

mmsecK

d lnA dT

10-3

K-1

Meff Da ΘM K


PMAA Gel in FeCl2



PMAA Gel in ferroin









4 Conclusion






References


Polym Sci A 50 68




4








5




Co(Rh) gamma

























2














constTATkcM

Ef

MBeff

)(ln3

ln22

2

(1)

constcM

Tk

eff

BSOD

2

3 (2)

















3



Sample δ mms

at 118K

Δ mms

at 118K

dδ dT

10-4

mmsecK

d lnA dT

10-3

K-1

Meff Da ΘM K


PMAA Gel in FeCl2



PMAA Gel in ferroin









4 Conclusion






References


Polym Sci A 50 68




4








5














constTATkcM

Ef

MBeff

)(ln3

ln22

2

(1)

constcM

Tk

eff

BSOD

2

3 (2)

















3



Sample δ mms

at 118K

Δ mms

at 118K

dδ dT

10-4

mmsecK

d lnA dT

10-3

K-1

Meff Da ΘM K


PMAA Gel in FeCl2



PMAA Gel in ferroin









4 Conclusion






References


Polym Sci A 50 68




4








5



Sample δ mms

at 118K

Δ mms

at 118K

dδ dT

10-4

mmsecK

d lnA dT

10-3

K-1

Meff Da ΘM K


PMAA Gel in FeCl2



PMAA Gel in ferroin









4 Conclusion






References


Polym Sci A 50 68




4








5








5

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Iron complexes embedding influence on PMAA hydrogel